The abrupt firing Tuesday of Secretary of State Rex Tillerson follows months of infighting between the State Department and White House over efforts by Tillerson to save the Iran nuclear deal and ignore President Donald Trump's demands that the agreement be fixed or completely scrapped by the United States, according to multiple sources with knowledge of the situation who spoke to the Washington Free Beacon.

In the weeks leading up to Tillerson's departure, he had been spearheading efforts to convince European allies to agree to a range of fixes to the nuclear deal that would address Iran's ongoing ballistic missile program and continued nuclear research.

While Trump had prescribed a range of fixes that he viewed as tightening the deal's flaws, Tillerson recently caved to European pressure to walk back these demands and appease Tehran while preserving the deal, according to these sources. The Free Beacon first disclosed this tension last week in a wide-ranging report.

White House allies warned Tillerson's senior staff for weeks that efforts to save the nuclear deal and balk on Trump's key demands regarding the deal could cost Tillerson his job, a warning that became reality Tuesday when Trump fired Tillerson by tweet.

Tillerson will be replaced by CIA Director Mike Pompeo, a former member of Congress who established a record as being tough on Iran and echoing many of the policies called for by Trump. Insiders expect Pompeo to take a much harder line on the nuclear deal and pursue many of the fixes advocated by Trump, such as outlawing Iran's ballistic missile program and instating fierce repercussions for any future breach.

While Tillerson's exit had been rumored for months, multiple sources with knowledge of the situation said the former secretary's repeated attempts to balk the White House and pursue his own diplomatic strategy, particularly regarding Iran, triggered his sudden exit.

Sources with knowledge of the matter said the White House informed Tillerson on Friday that Trump was seeking to make a change.

Rep. Ron DeSantis (R., Fla.), a member of the House Foreign Affairs Committee and vocal opponent of the nuclear deal, said he expects Pompeo to more faithfully execute Trump's policies regarding Iran.

"President Trump has been clear that the Iran deal is terrible policy and has sought ways to hold Iran accountable," DeSantis told the Free Beacon. "With Mike Pompeo, Trump will have a Secretary of State who sees the threat posed by the JCPOA [Joint Comprehensive Plan of Action] and by Tehran in a similar light as he does."

One veteran Iran policy expert who is close to the White House and worked repeatedly with the State Department told the Free Beacon that Tillerson worked to save the Iran deal as Trump was publicly advocating to scrap the agreement.

This tension between the White House and Foggy Bottom came to a head in recent days, prompting Trump to fire Tillerson and bring in Pompeo, an official who Trump believes will pressure European allies to more seriously fix a range of flaws in the nuclear deal.

"Tillerson staked his position on saving the Iran deal by threading the needle. He promised the president he could strengthen it enough to be good, but not so much the Europeans would backlash or the Iranians would bolt," said the source, who would only speak about the sensitive matter on background. "That was always going to be tricky, then it became impossible, then it became embarrassing. The Europeans weren't giving us enough on missiles and were refusing to budge on sunsets. And so here we are."

Opponents of the Iran deal on Capitol Hill welcomed the news of Tillerson's exit, telling the Free Beacon that as the deadline approaches for the United States and European allies to fix the Iran deal, Pompeo can help push Trump's hardline stance.

"As the deadline approaches to fix the Iran Deal, Tillerson's departure is welcome news. We need our top diplomat to share the president's view on the disastrous nature of the JCPOA, and CIA Director Pompeo is the right man for the job," said one senior congressional official who works on the Iran issue. "Hopefully now our European partners understand the president's resolve and will work with us to permanently prevent Iran from going nuclear."

Shortly after Trump fired Tillerson, the former secretary's spokesman issued a statement claiming Tillerson was not sure of the reason for his dismissal.

"The secretary did not speak to the president and is unaware of the reason," Steve Goldstein, undersecretary for public diplomacy, told reporters. Goldstein was fired later in the day due to his statement.

Sebastian Gorka, a former strategist and Deputy Assistant to President Trump, told the Free Beacon the White House had been laying the groundwork for Tillerson's departure since at least December of last year.

"This has been in the planning phase since at least December of last year and should come as a surprise to nobody," Gorka said. "The great things that were expected of Rex, especially in changing the America last culture at Foggy Bottom, did not happen, so this is a natural move."

Gorka praised Pompeo's work as CIA director and said "similar things are expected of him at the State Department."

Additionally, Gorka said, Pompeo "is loyal to the make American great again agenda."

Tillerson had been a source of tension for some time, according to insiders who explained the situation to the Free Beacon. The former Exxon executive gained a reputation for isolating top U.S. diplomats and even failing to return phone calls from senior officials such as David Friedman, the U.S. ambassador to Israel.

"There were serious problems, not only with Rex Tillerson isolating the Trump political appointees at State from his front office, but this was a secretary of state who wouldn't even return the calls of senior diplomats like our ambassador in Israel, and as such, his position was untenable."

Trump publicly acknowledged the discord in comments about the firing, saying that he and Tillerson did not often see eye-to-eye on key foreign policy matters.

Sources with knowledge of the president's thinking said that Tillerson's exit marks an effort by Trump to rid his administration of so-called "establishment figures" who openly worked at a crossroads with the president.

Tillerson's view that abandoning the nuclear deal would cause international tumult was cited by these sources as a key source of tension.

One senior former U.S. official with direct knowledge of the situation told the Free Beacon that Tillerson failed to properly read Trump's policy directives.

"It's very indicative of Tillerson to hear that he was surprised by the news because he has misread the president, failed to see cues all along, on policy and personal issues and has literally been in the dark from day one," said the official, who would only speak on background.

As Tillerson pursued his own agenda, United Nations Ambassador Nikki Haley emerged as one of Trump's most vocal boosters on Iran policy and efforts to scrap the deal.

"She stepped in that vacuum," said the former senior official. "She, to her credit, read the vacuum that the State Department had made with having Rex there."

At the end of the day, Tillerson failed to galvanize even his own staff behind his diplomatic efforts.

"I've watched so many secretaries of state come in, and even if I didn't agree with them, they had a base of support somewhere," noted the former official, who spent time working in the State Department. "I struggle to know what was Rex Tillerson's base of support. The elites in Washington didn't like him, the policy wonks didn't like him … he didn't have an audience with anyone, so it was inevitable he was going to be done."

Other White House insiders echoed this sentiment, telling the Free Beacon that Tillerson emerged as a roadblock to Trump's foreign policy strategy.

"Tillerson was an establishment figure, like Gary Cohn, and the president seems after a year to be tiring of them," said one source with knowledge of the matter. "He wants people closer to his own views. I think Tillerson's opposition on Jerusalem was a factor: it's not just that he opposed Trump but that he predicted violent reactions that didn't happen."

"I've got to figure that made the president wonder why he needed more such advice," the source said. "Same for the JCPOA and Tillerson's view that getting out of it would be a calamity."

Update 2:18 p.m.: This post has been updated with further information.