President Trump on Thursday accused an FBI agent who criticized him while serving on special counsel Robert Mueller's team of committing "treason" against the U.S.

In an interview with The Wall Street Journal, Trump argued that FBI agent Peter Strzok had plotted to undermine his presidency before he even came into office.

Strzok was once a key figure in the 2016 FBI investigation into former Secretary of State Hillary Clinton's handling of classified material. He was removed from the special counsel investigation into Russia's election meddling after it was discovered he exchanged anti-Trump text messages during the investigation with fellow FBI agent Lisa Page, with whom he was reportedly having an affair.

In one of those text exchanges, Strzok says that there's "no way" Trump gets elected but that if he does there needs to be an "insurance policy" in place because "we can't take that risk."

"A man is tweeting to his lover that if [Clinton] loses, we'll essentially do the insurance policy," Trump said in The Wall Street Journal interview. "'We'll go to phase two and we'll get this guy out of office.'"

"This is the FBI we're talking about - that is treason," Trump continued. "That is a treasonous act. What he tweeted to his lover is a treasonous act."

Trump's allies insist that the text messages are evidence that the FBI has been compromised by partisans who gave Clinton a pass and are eager to take Trump down.

There is some debate about what Strzok meant by taking out an "insurance policy," but he appeared to be referencing the investigation into whether Trump campaign officials had improper contacts with the Russians.

Trump has denied his campaign colluded in any way with the Kremlin.

"Of course there was no obstruction - there was no crime," Trump said in The Wall Street Journal interview. "They make up a crime, and the crime doesn't exist, and then they say obstruction."

Strzok was reassigned from the special counsel over the summer and relocated to the FBI's human resources department. Page, who referred to Trump as an "idiot" in the texts, also left the special counsel's team.

Both are expected to meet with House Intelligence Committee investigators about their involvement in the Trump and Clinton probes.