If you ask people around Washington about Rex Tillerson’s future, a preponderance of them will claim that his days as secretary of state are numbered. It’s not a matter of if he’s going to leave, but when.

Even before the New York Times reported last week that the White House is preparing to push Tillerson into early retirement and replace him with CIA Director Mike Pompeo, the consensus assessment in the Beltway was that the former ExxonMobil titan didn’t particularly enjoy his job anyway. He only reluctantly accepted the role of America’s top diplomat. Indeed, in his first long-form interview with the Independent Journal Review’s Erin McPike, Tillerson remarked, “I didn’t want this job. I didn’t seek this job…My wife told me I’m supposed to do this.”

With time, the job he never wanted became the job that wore him down. Tillerson has been browbeaten by the media, pummeled by retired career diplomats for the department’s horrendous morale and for his incompetence in triaging the bleeding of talent from the building, and criticized for defending the Trump administration’s recommended $10 billion cut to Foggy Bottom’s operations. Tillerson’s ties to President Trump—notwithstanding the president’s tweets of half-hearted support—never really recovered after he reportedly called his boss “a moron” to colleagues after a July national security meeting at the Pentagon.

Even within the State Department, Tillerson is generally looked upon with disgust. After news of the administration’s plan to eject Tillerson leaked, one current State Department official told Politico that because “Tillerson has been such a disappointment,” he was “looking forward to leadership that will support and advocate on behalf of the agency they lead instead of working so hard to undermine our efforts.”

Tillerson could be leaving for a variety of reasons. Take your pick: ineffectual leadership, lack of credibility and personal relationships where it matters, inter-administration squabbling over foreign policy, ire over being undercut by other members of the administration. But there’s another, more substantive, less petty reason that underlies all this: Iran.

Of all of the foreign policy issues that have grated on President Trump and his national security team, the Joint Comprehensive Plan of Action (JCPOA)—the agreement struck by the Obama administration that temporarily prevents Iran’s uranium enrichment capability—is the one that hurts the most. Trump has made no bones about wanting to tear it up and throw it in the garbage, beginning in the early days of his presidential campaign when he participated in a 2015 anti-JCPOA protest on Capitol Hill. To have Trump tell it, the nuclear deal with Tehran is the Munich of the modern era, a catastrophically stupid surrender to America’s principal adversary by a neophyte president who didn’t know the first thing about dealmaking.

Trump has always believed he could have extracted more concessions from the Iranians than Obama did. So when Secretary of State Rex Tillerson, Defense Secretary Jim Mattis, and National Security Adviser H.R. McMaster strolled to the White House back in July and recommended recertification of Iranian compliance, Trump wavered until the very last minute. The president ultimately agreed to the recommendation, but only after a task force was established from within the White House to prepare for de-certification when the next deadline came around in October.

The formation of that task force was undertaken as a repudiation of Tillerson’s State Department, which had failed to make the case for recertification. Three months later, Trump finally did what he wanted to do from the beginning: announce to the nation that the United States will no longer abide by “one of the worst and most one-sided transactions the United States has ever entered into.” If Tillerson was not a cabinet member, there is very good chance the JCPOA would have been decertified in July rather than October.

Mike Pompeo, the CIA director rumored to be under consideration for the secretary of state job, in many ways is the anti-Tillerson. As a former three-term congressman from deeply red Kansas who served as a member of the the Special Committee on Benghazi, he embraces the media and avidly plays the Washington game that so many of Tillerson’s detractors believe is instrumental to the State Department’s credibility in the national security bureaucracy. Whereas Tillerson is quiet, detached from the workforce he leads, and more concerned with the minutia of reorganizing the bureaucracy than setting policy, Pompeo doesn’t hesitate to sound and act political at times. While Tillerson ducks questions about Trump on the Sunday morning news shows, Pompeo has no issue defending his boss to the hilt in public. Speaking at the Reagan National Defense Forum last weekend, Pompeo said with a straight face that Trump’s tweets actually improve America’s intelligence gathering on foreign nations.

Pompeo has something else that Tillerson doesn’t have: he is about as hardline on Iran as a hardliner can possibly get. The CIA director remains the most intense opponent of the JCPOA in the Trump administration today (with Ambassador to the U.N. Nikki Haley a close second). On the topic of the Iran nuclear deal, Pompeo is John Bolton without the glasses and the mustache.

During his previous life on Capitol Hill, Pompeo used all the power he had as a congressman to prevent the JCPOA from surviving the congressional review process. He traveled to Vienna with Senator Tom Cotton—rumored to take over the CIA if Pompeo moves to Foggy Bottom—to meet with IAEA representatives and discovered a separate agreement between the IAEA and Iranian scientists on the issue of Tehran’s past nuclear work. After the disclosure, he sponsored and muscled through the House of Representatives a resolution that would have stopped all congressional deliberations on the JCPOA until the Obama administration delivered those side agreements to Congress. The message Pompeo hoped to send: by refusing to hand over the Iran-IAEA documents, President Obama was breaking the letter and spirit of the Iran Nuclear Agreement Review Act.

The fact that the JCPOA survived Congress only motivated Pompeo to make implementation of the agreement as difficult as possible. In January 2016, he offered legislation that would have ceased any U.S. sanctions relief to the Iranians unless and until the new administration submitted a series of detailed technical reports to Congress on the program 90 days prior. In order for sanctions relief to kick in again, Congress would have to formally pass a joint resolution through both chambers (the legislation didn’t go anywhere).

Three months later, he filed a bill that would have blocked the use of any U.S. funds to purchase excess heavy water from Iran, forcing Tehran to search for other buyers. And in a July 14, 2016 op-ed on FoxNews.com, on the one-year anniversary of the JCPOA’s signing, Pompeo advocated for the Obama administration to do the American people a service and walk away from it entirely. “Congress,” he wrote, “must act to change Iranian behavior, and, ultimately, the Iranian regime.”

The three-term congressman has taken all of that pugnacity to Langley. He’s built a positive rapport with Trump, briefing him on intelligence issues several days a week, and earned the president’s trust, friendship, and confidence. He’s an insider whose stock has risen every month he’s been on the job—while at the same time Tillerson’s capital has been plunging.

“Rexit” isn’t a done deal until it is. Tillerson has called the constant harping about his prospective resignation “laughable.” Trump has attempted to knock down reports of any discord between the two. Given Trump’s tendency to change his mind on a daily basis, Tillerson could very well last into 2018.

But whether “Rexit” happens next week or next year, Mike Pompeo will be the sure winner. And that can only mean one thing—a more ideological and less compromising Iran policy.

Daniel R. DePetris is a foreign policy analyst, a columnist at Reuters, and a frequent contributor to The American Conservative.