For a few weeks this winter, the biggest immigration news came not from Washington, D.C., but one of its affluent suburbs—Rockville, Maryland. Two Hispanic teenagers, one 18 and the other 17, were accused of raping a 14-year-old girl in a high school bathroom. The “Rockville rape case” became a staple of cable news and talk radio. White House press secretary Sean Spicer mentioned it in one of his daily briefings, citing the incident as an example of why President Trump’s commitment to stronger immigration enforcement was sorely needed.

“Part of the reason that the president has made illegal immigration and crackdown such a big deal is because of tragedies like this,” Spicer said in March. “Immigration takes its toll on our people if it is not done legally.”

Breitbart, the conservative website formerly associated with top Trump White House political strategist Stephen Bannon, ran several stories highlighting the gory details of the rape allegations. One reported that, according to police, “the suspects allegedly forced a girl to perform oral sex on them in a bathroom stall while they raped and sodomized her, despite her crying out in pain, begging them to stop.”

The older of the two alleged assailants was Henry E. Sanchez-Milian, a Guatemalan who U.S. Immigration and Customs Enforcement said was caught illegally crossing the border from Mexico just a few months earlier. He had been issued a notice to appear before an immigration judge for a deportation hearing, according to the agency.

Then in May the rape charges against the two were dropped. Montgomery County State’s Attorney John McCarthy announced that after a “painstaking investigation” it was concluded that “the original charges cannot be sustained” and prosecution is “untenable” due to lack of corroboration and “substantial inconsistencies” in the girl’s story.

Supporters of lenient immigration enforcement hailed the dropped charges as vindication and decried the controversy as an example of the kind of anti-immigration hysteria fostered by President Trump, along with his deputies and voters. The White House was pressed on whether Spicer’s hasty judgment reflected a desire merely to justify Trump’s immigration policies. But the White House rejected the allegation. “I think we’re always looking to protect the American people,” said deputy press secretary Sarah Huckabee Sanders during a press briefing. “Sean was speaking about what he knew at the time… I’m not going to retract anything without further information.”

But Journalist Robby Soave, writing in the libertarian magazine Reason, quipped that the Rockville rape case “should now be known as the Rockville rape retraction.” He chided conservatives for clinging to the rape allegations in the face of the dropped charges and added that “right-wing pundits should be eating crow.”

Not surprisingly, immigration control advocates found the morality tale more complicated. Yes, the rape charges were dropped. Such allegations are hard to prove. But you have one already potentially deportable illegal immigrant who is being charged with possession of child pornography, and the two clearly were engaged in behavior that was inappropriate if not verifiably criminal. Two men in their late teens were enrolled in the ninth grade at the school.

Beyond the emotions generated by the case and the intractable nature of the underlying issue, the episode reflects the legal and political complexities unleashed by the emergence of so-called sanctuary cities. This is a designation given to local governments that refuse to cooperate with federal immigration enforcement, largely by declining to identify illegal immigrants with whom they come into contact. Rockville considers itself to be such a sanctuary jurisdiction, and officials there were deliberating about whether to formalize this policy when the case involving the teens became national news.

Trump set himself foursquare against such policies throughout his campaign. “We will end the sanctuary cities that have resulted in so many needless deaths,” Trump vowed at one point. “Cities that refuse to cooperate with federal authorities will not receive taxpayer dollars, and we will work with Congress to pass legislation to protect those jurisdictions that do assist federal authorities.”

Trump’s most commonly cited example was Kate Steinle, a young woman who was, as Trump put it, “gunned down in the sanctuary city of San Francisco by an illegal immigrant deported five previous times.’’ Steinle has been the namesake of many state and federal legislative measures seeking to end sanctuary city policies as an unjustifiable impediment to immigration law enforcement.

As many as 300 municipalities are considered sanctuary cities, though they vary in the degree to which they embrace the label. Contrary to the phrase’s implications, they cannot stop the federal authorities from enforcing the law. But they can make it more difficult and thus effectively thwart deportations. The most commonly accepted definition of a sanctuary city is the refusal of local jurisdictions to enforce detainer orders issued by federal immigration authorities. These are requests for local governments to hold suspected illegals so federal officials can arrest and ultimately remove them.

Over the 19-month period from January 1, 2014, to September 30, 2015, reports an immigration-restriction think tank called the Center for Immigration Studies, more than 17,000 detainers were rejected by these jurisdictions. “Of these,” says the organization, “about 11,800 detainers, or 68 percent, were issued for individuals with a prior criminal history.” That’s because the subjects of these detainers are frequently criminal aliens in local custody for non-immigration-related offenses. Cooperation between federal and local law enforcement greatly expedites the removal of illegal immigrants, and people in city and county jails constitute the subset of the undocumented population that draws the least political sympathy. Politicians of both parties often say they favor their deportation.

Sanctuary cities have emerged as a major political flashpoint in the incendiary immigration issue. The Trump administration wants to attack them in its fight to step up immigration enforcement and sharply curtail the number of unauthorized immigrants living in the United States. Liberal jurisdictions, meanwhile, celebrate their status as sanctuary cities in order to align themselves with the anti-Trump “resistance.” This includes big Democratic cities such as Chicago and New York.

But the proliferation of sanctuary cities has more than just political consequences. The Pew Research Center found that 61 percent of the estimated 11 million illegal immigrants in the United States live in 20 major metropolitan areas. Seventeen of them are considered sanctuary cities.

The Trump administration has plenty of room to increase deportations even with all the sanctuaries. It has expanded the category of criminal aliens who get enforcement priority. Its rhetoric and reputation alone have decreased border crossings and encouraged some illegal immigrants to “self-deport,” in the infamous phrase of 2012 Republican presidential nominee Mitt Romney.

After the repeated failure of comprehensive immigration reform legislation in the House—better known to opponents as “amnesty”—late in the George W. Bush administration and early in Barack Obama’s, it was concluded that the federal government lacked sufficient credibility on the issue to pass a comprehensive bill. Officials of both parties accepted the view that the government needed to project a tougher stance against illegal immigration before any serious bill could clear Congress.

This political reality was hardened also by the results of the 1986 “amnesty” legislation passed on a bipartisan basis and signed into law by Ronald Reagan. It not only failed to deliver on its enforcement promises but also seemed to open the way for an even greater influx of illegals. Thus did President Obama in particular boast of “record deportations” toward the beginning of his administration. “For us, this president has been the deporter-in-chief,” National Council of La Raza president Janet Murguía complained in 2014.

But immigration restrictionists weren’t mollified. They argued that Obama was “cooking the books” on deportations. The administration, these critics complained, routinely counted people apprehended at the border as deportations, a break with normal protocol. At one point, to reach their goal for total deportations, administration officials included 19,000 people who had actually left the country the previous fiscal year.

Ironically, the Obama administration also relied heavily on cooperation from local law enforcement, established initially under the Bush-era Secure Communities program, which increased collaboration with the Department of Homeland Security and the Justice Department to identify illegal immigrants already in custody for potential removal. This program also helped Obama officials boost deportation numbers.

Yet as Obama’s time in office wore on, prospects for passing an immigration bill never improved (especially after Republicans captured a House majority in the 2010 midterm elections), and pressure grew from Latino and immigrant-rights activists to back off on deportations. Just as conservatives were becoming more restrictionist in outlook, progressives began to demand “not one more deportation.”

The Obama administration responded to this by considerably loosening its enforcement posture. The president promulgated a pair of controversial executive orders essentially declaring “Dreamers,” or young undocumented immigrants brought into the country as children, off limits for deportation. More generally, only illegal immigrants convicted of serious, usually violent, crimes were a major enforcement priority.

The 2011 “Morton Memos,” issued by ICE Director John Morton to spell out these liberal enforcement priorities, were liberalized further in 2014. The top deportation priorities were terrorists and national security threats, convicted gang members, illegal border crossers caught in the act, and convicted aggravated felons. Repeat and significant misdemeanor offenders were only a secondary priority.

“We’re going to keep focusing enforcement resources on actual threats to our security,” Obama said at the time. “Felons, not families. Criminals, not children. Gang members, not a mom who’s working hard to provide for her kids.”

In a 2012 presidential debate with Romney, Obama also said immigration authorities should “go after folks who are criminals, gang bangers, people who are hurting the community…not after folks who are here just because they’re trying to figure out how to feed their families.”

Most would agree that these illegal immigrants should be at the top of the list for removal from the country. But the Migration Policy Institute estimated that under the 2014 guidelines, 87 percent of illegal immigrants in the United States were not a high priority, up from 73 percent under the original Morton Memos from three years prior.

Pro-immigration activists protested that the Obama administration wasn’t quite that permissive in practice. The Marshall Project, a left-leaning journalism outfit that focuses on criminal justice issues, analyzed the ICE data on some 300,000 deportations that took place between Obama’s November 2014 speech and April 2016. The group concluded that 60 percent involved people with no non-immigration-related offenses, and another 11 percent were drug-related.

Still, deportations were down by about 20,000 in fiscal 2014, according to a Pew analysis of Department of Homeland Security data. That was powered by a 16 percent drop in deportations of illegal immigrants who were convicted of a crime. Criminal deportations declined 60 percent between a 2011 peak and 2016.

By September 2015 deportations had fallen to the lowest levels since 2006. “Last year’s removal and return statistics are characterized prim arily by three things: first, last year’s removal numbers reflect this Department’s increased focus on prioritizing convicted criminals and threats to public safety, border security and national security,” Department of Homeland Security Secretary Jeh Johnson said in a statement at the time.

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Trump aggressively campaigned against Obama—and Hillary Clinton—on immigration. “Countless Americans who have died in recent years would be alive today if not for the open border policies of this administration,” Trump said in a major August 2016 immigration speech in Arizona. He went on to identify some of them. “[T]here is the case of 90-year-old Earl Olander, who was brutally beaten and left to bleed to death in his home,” Trump continued. “The perpetrators were illegal immigrants with criminal records who did not meet the Obama administration’s priorities for removal.”

After Trump’s election he sought to make good on his immigration-related campaign promises. His administration rescinded the Obama-era enforcement directives and replaced them with much stricter standards. The new president awarded the Justice Department to Jeff Sessions, a Republican senator from Alabama who was the leading immigration restrictionist on Capitol Hill and a major influence on Trump’s own position on the issue. That put the new attorney general in charge of the second most important cabinet-level department when it comes to immigration. He also took a strong stand against sanctuary cities.

“[T]he Department of Homeland Security recently issued a report showing that in a single week, there were more than 200 instances of jurisdictions refusing to honor Immigration and Customs Enforcement detainer requests with respect to individuals charged or convicted of a serious crime,” Sessions said in a speech earlier this year. “The charges and convictions against these aliens include drug trafficking, hit and run, rape, sex offenses against a child, and even murder.”

In continuing to prioritize criminal aliens for removal, Trump has expanded the number of people who would be so considered. Illegal immigrants convicted of any criminal offense, charged with a criminal offense, guilty of defrauding any public benefits program or government agency, or who pose a national-security threat, can all be removed. And, unlike the Obama policy, there is no hierarchy of priorities; all are in theory equally deportable.

Many immigration experts believe the upshot of the Trump administration’s enforcement priorities is that illegal immigrants who are easily within reach will be first in line for deportation. That means there will be enough low-hanging fruit left over from the Obama years to foster increased deportations despite the sanctuary cities’ best efforts. But the sanctuary cities will complicate things eventually as more of the undocumented population seeks refuge inside them.

“This is the Trump era,” Sessions said in a statement focused on sanctuary cities. “Progress is being made daily, and it will continue. This will be the Administration that fully enforces our nation’s immigration laws.” The administration had issued an executive order stripping some federal funding from designated sanctuary jurisdictions.

But getting rid of sanctuary cities won’t be easy. The liberal and pro-immigration sentiments driving the move toward sanctuary policies are very powerful throughout much of the country. Beyond that, even many natural allies of the Trump administration will balk at the move. First and foremost are law enforcement officials in some immigrant-heavy cities. They fear the undocumented population has become too integrated with the legal populations of many ethnic neighborhoods, and having residents of these neighborhoods fear deportation whenever they interact with the local police makes it harder to solve crimes and protect the community.

And some jurisdictions become sanctuary jurisdictions not by choice but by threat of lawsuit. Some officials in these localities believe that they are on legally shaky ground if they hold suspected illegal immigrants at federal authorities’ request without a valid court order. In 2014, a federal judge ruled that a local jail in Oregon violated a woman’s civil rights by complying with a detainer request without court approval.

A Stateline report late last year highlighted rural Sioux County, Iowa, where 82 percent of the vote went to Trump, who also won statewide. The sheriff publicly states that he does not wish to make his jurisdiction a sanctuary county. But judicial rulings like the one in Oregon keep him, as a matter of policy, from detaining suspected illegals without a court order.

The Trump administration also has limited options when it comes to forcing cities and counties to comply with its immigration measures. Technically, while sanctuary cities may be violating the spirit of the law, the local cops aren’t immigration agents. Most federal legislation aimed at stopping these practices would employ the tactic of denying federal funding to local authorities who refuse to cooperate with immigration enforcement. But the withholding of federal funds must be tied to the activity involved, and the monetary leverage here is less potent than in other areas. If a state adopts a drinking age below 21, for example, Washington can deny federal highway funds, a powerful incentive. The incentives attending immigration policy are much less powerful.

Further, the courts haven’t been favorably disposed to Trump on immigration policy, as evidenced by the fate of his “travel ban” affecting at least a half dozen Muslim-majority countries. It has been held up in legal tangles since the beginning of his term. The administration’s efforts against sanctuary cities haven’t fared much better. In April a federal court held up the administration’s policy defunding sanctuary cities. “The Counties have demonstrated that they are likely to succeed on the merits of their challenge to Section 9(a) of the Executive Order, that they will suffer irreparable harm absent an injunction, and that the balance of harms and public interest weigh in their favor,” wrote Judge William Orrick.

The Trump administration in May appeared to concede that its options were limited when the Justice Department under Sessions adopted a narrow definition of sanctuary cities for the purpose of withholding federal funding. Only cities, counties, and towns that violate a federal law requiring sharing information on immigrants’ legal status would be in jeopardy of losing funding, the Justice memo said.

That means the Trump executive order would not apply to communities that refuse to comply with detainers, so most places considered sanctuary cities would still be eligible for the Justice Department grants. But not all immigration hawks viewed this as a capitulation.

Jessica Vaughan, policy director at the Center for Immigration Studies, denied that this represented much of a retreat. “It says that in order to receive certain federal funds from DOJ and DHS, jurisdictions need to be complying with the federal law on sanctuary policies. If anything, it is an expansion on the initiative already in motion against the sanctuaries.’’ She explains that the initial action applied only to DOJ grants, while the Sessions memo adds DHS.

And the memo hinted the administration had further actions in mind. “While the Executive Order’s definition of ‘sanctuary jurisdiction’ is narrow, nothing in the Executive Order limits the Department’s ability to point out ways that state and local jurisdictions are undermining our lawful system of immigration or to take enforcement action where state or local practices violate federal laws, regulations, or grant conditions,” Sessions wrote.

Vaughan adds that, while some anti-enforcement advocates believe jurisdictions that do not honor detainers are now home free, that isn’t necessarily true. She says that the DOJ’s investigation into sanctuary policies found that failure to comply with detainers can also adversely affect ICE’s ability to enforce the law, thus giving added potential leverage against such jurisdictions. “I am sure all of this will be litigated,” she predicts. Vaughan said that the next thing to watch is whether the Justice Department follows through with the nearly 10 sanctuary jurisdictions they threatened to defund last year. They had until June 30 to comply with the department’s directive or pay back the grants they have received last year. How many will actually be sanctioned by Justice? “That will be interesting,” she said.

Also, Trump isn’t alone in moving against sanctuary cities. He has allies on Capitol Hill. Sens. Luther Strange, R-Ala., and David Perdue, R-Ga., have brought forth legislation that would cut federal transportation and infrastructure spending for local areas whose governments refuse to cooperate on immigration enforcement. That gets closer to the state drinking age example. Strange succeeded Sessions in the Senate, while Perdue and Sen. Tom Cotton, R-Ark., seem to be in competition to become Sessions’s main replacement as Congress’s foremost immigration restrictionist. They would withhold from sanctuary cities money from one transportation program that has given out $5 billion since it was started in 2009 and a second one expected to dole out $4.5 billion over the next three years.

That’s relatively small potatoes compared to overall federal highway funds. But it expands the pot of money sanctuary cities are giving up from Homeland Security and Justice Department grants. It also counters liberal state legislators who want to deny money to any contractors who work on Trump’s proposed border wall. “Sanctuary cities are threatening to penalize their own taxpaying local businesses if they submit plans to help enhance our border security with a wall,” Perdue said in a statement. “Our nation is a nation of laws. Until these cities join the rest of us in following these laws, they have no business receiving federal grant funds.”

While much of the onus for action against sanctuary cities remains on the Trump administration, which is embattled on multiple fronts, immigration restrictionists expect the executive branch to rise to the occasion. “The attorney general’s move is a very positive one, and I’m sure it’s not his last move against the sanctuaries,” says Vaughan. It likely wasn’t the last move for the rest of the administration either. When the president’s first federal budget proposal was unveiled, burrowed deep within the dense document were proposals to expand the definition of sanctuary cities from the narrow one recognized by the Justice Department and expose more jurisdictions to the risk of losing funds. The budget calls for defunding local entities that don’t comply with detainers. The Justice Department has already threatened nine jurisdictions with cuts. Under these rules, the numbers would likely exceed 100.

The budget also would make it easier to withhold the money in other ways. “The Secretary of Homeland Security or the Attorney General may condition a grant or cooperative agreement awarded by the Department of Homeland Security or the Department of Justice to a State or political subdivision of a state, for a purpose related to immigration, national security, law enforcement, or preventing, preparing for, protecting against or responding to acts of terrorism,” the document reads.

Though presidential budget proposals don’t necessarily become law, this Trump language reflects the president’s determination to bring states and localities to heel on the issue of sanctuary policies designed to thwart the federal enforcement of immigration laws. His determination is matched, however, by the strong pro-immigration sentiments that generated these sanctuary policies in the first place.

Trump’s election is both a symptom and cause of great national polarization. Thus it shouldn’t be any surprise that his election has exposed yet another division: between, on the one hand, states and localities that want to cooperate with his proposed immigration crackdown and, on the other, growing numbers of liberal enclaves that will use whatever powers they have at hand to defy it.

W. James Antle III is politics editor of the Washington Examiner and author of Devouring Freedom: Can Big Government Ever Be Stopped?