Former FBI Director James Comey, a frequent detractor of President Donald Trump, denounced as "dumb lies" Trump's assertions that there was an FBI conspiracy to sabotage his 2016 presidential campaign.

In an op-ed published online by the Washington Post Comey pushed back on Trump's claims that the FBI tried to take down his campaign by spying on it during the 2016 election cycle.

"There was no corruption. There was no treason. There was no attempted coup. Those are lies, and dumb lies at that," Comey wrote. "There were just good people trying to figure out what was true, under unprecedented circumstances."

The op-ed comes after Trump has repeatedly accused the FBI of spying on his 2016 campaign in an effort to sabotage his presidential bid. He has called for an investigation into the spying and the origins of special counsel Robert Mueller's probe into Russian interference in the 2016 presidential election.

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Comey said that Trump can "investigate the investigators," but when it is over, "you will find the work was done appropriately and focused only on discerning the truth of very serious allegations.

In a tweet earlier this month, Trump claimed that his 2016 campaign was "conclusively spied on," adding "TREASON means long jail sentences, and this was TREASON!"

In addition, in April Attorney General William Barr at a congressional hearing, without providing evidence, said "I think spying did occur" on Trump's 2016 campaign. And Barr has more recently made similar suggestions in media interviews. In the same congressional hearing, Barr also said that he would be looking into the "genesis and the conduct" of the FBI's investigation into ties between the 2016 Trump campaign and Russia.

Trump last week ordered U.S. intelligence agencies to cooperate with Barr's investigation "into surveillance activities during the 2016 Presidential election." The attorney general was also given the authority to declassify information related to that investigation.

However, the former FBI director's comments also come ahead of a report from Justice Department Inspector General Michael Horowitz, who last year initiated an investigation into possible abuses of foreign intelligence surveillance authority by the FBI.

Comey in his op-ed defended the FBI's decision to investigate how a foreign policy adviser to the Trump campaign "talked to a Russian agent in London" in April 2016 and "learned that the Russians had obtained 'dirt' on Hillary Clinton in the form of thousands of emails." He said no one from the Trump campaign told the FBI about the interaction and he found out about it in July 2016 from an "allied ambassador."

"But when we finally learned of it in late July, what should the FBI have done? Let it go? Go tell the Trump campaign? Tell the press? No," Comey wrote. "Investigate, to see what the facts were. We didn’t know what was true."

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Former top FBI lawyer James Baker has also recently defended the origins of the Russia investigation, saying it was opened for "lawful, legitimate reasons," according to CNN.

Comey also pushed back against Trump's comments that former FBI agent Peter Strzok tried to take down the president's 2016 campaign. Anti-Trump text messages from Strzok and former FBI lawyer Lisa Page were uncovered in 2017.

The former FBI director noted that Strzok had not revealed the FBI's investigation into the interaction between the Trump foreign policy adviser and Russian agents, and had also written the letter announcing that the investigation into Hillary Clinton's private email server was re-opened.

"There’s the first problem with Trump’s whole 'treason' narrative," Comey wrote. "If we were “deep state” Clinton loyalists bent on stopping him, why would we keep it secret?"

"We investigated. We didn’t gather information about the campaign’s strategy. We didn’t 'spy' on anyone’s campaign," Comey continued.

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