For months, the Fox News Channel host Tucker Carlson had been lobbying President Donald Trump to fire John Bolton, telling him it was foolish to keep on his team a top adviser who did not share his views on pressing national security issues.

Carlson and a host of others, including several senior administration officials, frequently told Trump that Bolton, a career hawk with a reputation as a vicious bureaucratic infighter, not only wasn’t on his team but was using the news media against him.

Trump, who became a fan of his future national security adviser while watching his frequent television appearances on Fox, told these people that he enjoyed Bolton’s presence in negotiations because he believed he spooked U.S. adversaries like Iran. But he chafed at reading about and watching news reports of Bolton’s disagreements with administration policy on everything from talks with North Korea to pulling troops out of Syria to angling for a sitdown with Iranian leaders.

“Where there is public disagreement like that and it keeps going on from one issue to another, I do think there is a cumulative effect on the human psyche and it probably leads to less communication,” said Gen. Jack Keane, the former Army vice chief of staff who talks frequently with the president and other senior administration officials.

Ultimately, it was hearing media accounts about how Bolton had advised the president to scuttle a meeting with Taliban leaders at Camp David that proved a breaking point for Trump, according to sources in and out of the administration. In the president’s telling, he had taken his own counsel in arriving at the decision to call off the meeting and end the negotiations, and he was infuriated to hear Bolton credited with influencing his decision.

Bolton’s exit is a stark illustration of how Trump has grown increasingly confident in his own judgment on national security — and how he’s developed a greater sense of urgency to follow through on his campaign promise to reduce U.S. entanglements abroad. Bolton saw things differently and made little secret of it. Both men were equally firm in their convictions, and the conflict proved irreconcilable.

A Bolton spokesman did not reply to a request for comment, but this account is based on conversations with nearly a dozen administration officials and people close to the president.

Bolton’s critics, including Carlson, also used the incident to urge the president to act. He was a leaker, they told him. Others in the administration feared the same, at times excluding Bolton and his allies from sensitive meetings for fear they would weaponize the information exchanged to their advantage.

While Bolton’s predecessor, H.R. McMaster, had worked to adhere to a traditional process where the president is presented a range of options on key issues, along with a list of risks associated with each option, Bolton operated differently, preferring instead to give the president his own guidance in private. While many had griped that McMaster held too many meetings, under the Bolton regime, Secretary of State Mike Pompeo at one point joked with colleagues about jump-starting his own National Security Council process to fill the Bolton void.

Bolton, the president’s third national security adviser, was never a natural fit in the Trump White House. Serious and cerebral, the 70-year-old Yale-trained lawyer immediately went about assembling a team of like-minded loyalists immensely capable of pushing his policy priorities — which were sometimes, but not always, those of his boss.

While Bolton has served effectively in the senior ranks of previous administrations, after Trump passed him over to be secretary of state during the transition in 2016, Bolton widely acknowledged that this was likely to be his last — and most senior — government post. That meant that unlike some of his colleagues, most notably Pompeo, who is 55, he had little to lose by aggressively pursuing some of his own policy priorities, be it sticking it to Iran or dismantling the International Criminal Court, even if the president didn’t share them.

As with previous top foreign-policy aides including McMaster and Rex Tillerson — and even James Mattis, who resigned of his own volition — substantive disagreements and stylistic differences simply led the president to seek Bolton’s advice less frequently.

“The handwriting’s been on the wall for a long time. You can think back to John Bolton literally being sent to Mongolia at the time that Trump was having his last meeting with Kim Jong Un, which is, you know, being sent to Mongolia is kind of a joke, right?” said David Rothkopf, who has written extensively about the NSC. (Trump brought Carlson, the Fox News host, along with him instead.)

Even Bolton’s dismissal instantly became a matter of dispute between the two men — going public just moments after the president announced his departure. Bolton was left to fume privately to allies that Trump had mischaracterized the events that led to his exit, and publicly to reporters seeking to illuminate the nature of their dispute.

While the president said in a tweet that he had asked for Bolton’s resignation on Monday evening, Bolton told ABC News’ Jonathan Karl that Trump was “flatly wrong.”

“He never asked me to resign directly or indirectly,” Bolton said. “I slept on it and resigned this morning.”

While Bolton’s deputy, Charles Kupperman, was on Tuesday named acting national security adviser, few in the White House believed the longtime Bolton acolyte would remain in that position for the long term, and the president said he would name a permanent replacement next week.

Among the names being floated for the position are Stephen Biegun, currently the U.S. special representative for North Korea, who was previously considered for the position, and the retired Army Col. Douglas MacGregor, a frequent guest on Carlson’s program.

Sen. Lindsey Graham (R-S.C.) told the Fox News Channel’s Bret Baier on Tuesday evening that the president had also said he was considering the vice president’s national security adviser, Keith Kellogg; Brian Hook, currently the special envoy for Iran; and Ricky Waddell, an assistant to the chairman of the Joint Chiefs of Staff and an NSC veteran.

But critics cautioned that the president’s fourth national security adviser is likely to have little sway with the president.

“The next national security adviser of the United States is going to be Donald Trump, just like the current national security adviser of the United States is in fact Donald Trump,” Rothkopf said. “The next national security adviser is going to have [the job] in name only.”