Ever since Strom Thurmond shuffled off to an Edgefield retirement home over a decade ago, Lindsey Graham has represented South Carolina—and served as John McCain’s junior partner—in the Senate.

Like McCain, Graham has been bipartisan in his deal-making and support for war-making. What he has lacked in conservative fervor for Grover Norquist’s no-tax-hike pledge or immigration enforcement, he has compensated for as a national-security tough guy who champions the military in his state.

South Carolina is home to eight military bases and two military colleges. More than a fifth of voters in the state’s 2012 Republican presidential primary served in the armed forces. Graham is still a U.S. Air Force reservist, holding the rank of colonel and serving as senior instructor for the Judge Advocate General’s Corps, though he has never been in combat.

Graham is here again following in the footsteps of his predecessor. Thurmond, who glided onto the beaches of Normandy during the D-Day invasion at age 42, served in the reserves as a sitting senator. He chaired the Senate Armed Services Committee in his 90s.

So it is remarkable that two of Graham’s three challengers in next year’s Republican primary seem prepared to take the senator’s hawkishness head-on. State Sen. Lee Bright, a lawmaker from Greer, endorsed Ron Paul for president in the Palmetto State’s pivotal primary. Bright’s campaign website blasts the slogan, “For Senate, for liberty.”

Bright is joined by Charleston businesswoman Nancy Mace. When Graham suggested that Rand Paul was soft on national defense, Mace decided to stand with Rand. She argued that instead of endorsing “President Obama’s intrusive arm of big brother regarding the collection of data and phone records,” we might instead revisit Graham’s policies of foreign aid and intervention.

“Most would agree with Senator Graham that radical Islam is the foremost threat to our nation’s security,” Mace continued. “However, if we are truly protecting Americans from this grave threat, then how does it make sense to supply arms and aid to countries who support radical Islam, bring harm to our allies, burn our flag, hate our culture and allow terrorists to plot against the United States and her friends?”

Bright went a step further. “I think the federal government is a lot more dangerous to our liberties and our freedoms than some radical Islamist coming in,” he told a conservative website, saying that vigilance was required but Graham has “got more faith and trust in the federal government than I do” regarding national surveillance.

In years past, this would seem an improbable path to unseating a sitting GOP senator in South Carolina. But the political terrain has shifted somewhat under Graham’s feet. The entire state House delegation, Republican and Democrat, voted with Justin Amash—and thus Bright and Mace—on the NSA surveillance program.

Mick Mulvaney, Mark Sanford, and Jeff Duncan are three Republican congressmen from the state who have clashed with McCain-Republicans on occasion. New Sen. Tim Scott supported Rand Paul’s drone filibuster. State Sen. Tom Davis joined Bright in endorsing Ron Paul for president before last year’s primary.

South Carolina has also become more willing to revolt against the party establishment. In 2012, local Republicans broke their long string of support for the national frontrunner by being one of only two states to vote for Newt Gingrich. Former Sen. Jim DeMint, now president of the Heritage Foundation, actively recruited and raised money for primary challengers running against his colleagues.

Graham is not going to go away quietly, however. He is sitting on at least $6.3 million in cash on hand. While his job approval rating has tumbled, it remains a respectable (if not insurmountable) 57 percent. Late last year, Public Policy Polling found enthusiasm for a conservative primary challenge to Graham cooling.

Finally, Graham’s approach to intraparty politics is similar to his foreign policy: always spoiling for a fight. Many Republicans who have lost to Tea Party challengers have behaved as if it is beneath them to engage their opponents. Graham will relish doing so, taking a page out of McCain’s playbook against J.D. Hayworth in 2010.

Graham is sure to try to make his primary opponents look like pacifists at best, Jane Fonda impersonators at worst.

That will be quite an undertaking against Mace, the first woman to graduate from the Citadel, the state’s military college. Mace’s father, retired Brigadier Gen. James Mace, is also a highly decorated Citadel graduate.

It also remains to be seen how the number of challengers impacts the race. Because there will be a runoff if no candidate reaches 50 percent, the risk is less that the anti-Graham vote will be split than that divided resources—and infighting—will prevent either Bright or Mace from becoming viable. But a runoff strategy in a crowded primary field worked for Ted Cruz in Texas.

The primary will nevertheless be an interesting pre-2016 test of whether the GOP is still Graham’s old party.

W. James Antle III is editor of the Daily Caller News Foundation and author of Devouring Freedom: Can Big Government Ever Be Stopped?