Strzok was integral to two of the bureau’s most high-profile recent investigations: the Russia case, and the investigation into Hillary Clinton’s use of a private email server while secretary of state.

But when a Justice Department inspector general investigation uncovered politically charged messages that Strzok had exchanged with another FBI official, he was relegated to a position in human resources.

Conservatives soon made Strzok the target of their attacks against the special counsel investigation into the president’s campaign, and the FBI took steps to remove him from its ranks.

Strzok’s position in the bureau had been precarious since last summer, when Inspector General Michael Horowitz told Special Counsel Robert Mueller that the lead agent on his team had been exchanging anti-Trump messages with an FBI lawyer. The next day, Mueller expelled Strzok from the group.

The lawyer, Lisa Page, had also been a part of Mueller’s team, though she left a few weeks earlier and no longer works for the FBI. She and Strzok were having an affair.

US President Donald Trump has derided the pair as “FBI lovers”, and he and his conservative allies have pointed to their conduct in an attempt to discredit the Mueller probe. As recently as Saturday, Trump tweeted an attack on Strzok, Page, former FBI director James B. Comey and deputy FBI director Andrew McCabe, all of whom have been fired or otherwise departed the FBI in the last 15 months.

“Will the FBI ever recover it’s once stellar reputation, so badly damaged by Comey, McCabe, Peter S and his lover, the lovely Lisa Page, and other top officials now dismissed or fired?” Trump wrote. “So many of the great men and women of the FBI have been hurt by these clowns and losers!”

Horowitz concluded that Strzok showed a “willingness to take official action” to hurt Trump’s electoral prospects, particularly in a text he sent telling Page “we’ll stop” Trump from being president.

Strzok, who was a deputy assistant director for counter-intelligence at the bureau, has apologised for sending the messages and said they reflected personal views that did not affect his work.

His lawyer has said that had Strzok wanted to prevent Trump’s election, he could have leaked that Trump’s campaign was under investigation for possibly coordinating with Russia – a revelation that might have upended his bid to become president.

At a congressional hearing earlier this month, Strzok sparred with Republican lawmakers who raised questions about his character and even his marriage. He asserted there was “no evidence of bias in my professional actions” and that his having to testify was “just another victory notch in [Russian President Vladimir] Putin’s belt and another milestone in our enemies’ campaign to tear America apart”.

Strzok was escorted out of the FBI building in June and effectively relieved of work responsibilities, though he technically remained an FBI employee as he and his lawyer challenged the effort to dismiss him. On July 24, they made a final pitch to Candice Will, who leads the FBI’s Office of Professional Responsibility.

Goelman said Will ultimately decided that Strzok face a demotion and 60-day suspension and be subjected to a “last-chance agreement”. That would have put him on thin ice if he were commit another offence. But Goelman said Bowdich overruled that decision and ordered Strzok’s termination.

During a June congressional hearing, FBI Director Christopher Wray said Strzok had been referred to the Office of Professional Responsibility – which he referred to as the bureau’s “independent disciplinary arm” – and that officials would “not hesitate to hold people strictly accountable”.

Wray promised that process would be “done by the book”.

Strzok is the third high-ranking FBI official involved in the Clinton and Russia investigations to be fired amid an intensely political backdrop.

Trump removed Comey as the bureau’s director and said he did so thinking of the Russia case. Attorney General Jeff Sessions later removed Comey’s deputy, McCabe, after the inspector general contended that he lied about a media disclosure related to Clinton.

McCabe – who, unlike Comey, could not be removed at the will of the president – has said his termination was a politically motivated attempt to undermine the Mueller probe. He is currently facing a criminal investigation by prosecutors in the DC US Attorney’s Office.

It is possible that others could yet face discipline. The inspector general identified five FBI employees, including Strzok and Page, with some connection to the Clinton email case who had exchanged messages expressing hostility toward Trump, support for Clinton or other political views.

Each was referred to the FBI for possible violations of the bureau’s code of conduct.