Former FBI director and long-time Republican supporter James Comey is urging American voters to support Democrats in the upcoming midterm elections.

“This Republican Congress has proven incapable of fulfilling the Founders’ design that ‘Ambition must … counteract ambition,’” Comey said in a tweet late Tuesday.

“All who believe in this country’s values must vote for Democrats this fall. Policy differences don’t matter right now. History has its eyes on us.”

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Comey’s tweet comes as tensions continue to boil over in Washington, following President Donald Trump’s extraordinary press briefing alongside his Russian counterpart in Helsinki on Monday.

Speaking next to Russian President Vladimir Putin, Trump repeatedly rejected the conclusions of the U.S. intelligence agencies and failed to publicly condemn Russia for allegedly meddling in the 2016 election.

“They said they think it’s Russia,” Trump said of the U.S. intelligence community, before adding: “I have President Putin … he’s just said it’s not Russia. I will say this, I don’t see any reason why it would be.”

On Tuesday, however, Trump said he misspoke in Helsinki, and that he had, in fact, meant to say he didn’t see “any reason why it wouldn’t be Russia,” thereby tilting the scales in favor of the assessment reached by his own intelligence agencies, and not the denial issued by Putin.

Comey, who has frequently criticized the U.S. president since being fired in May 2017, had spoken out against Trump’s comments in a separate tweet on Monday.

“This was the day an American president stood on foreign soil next to a murderous lying thug and refused to back his own country. Patriots need to stand up and reject the behaviour of this president,” Comey said via Twitter on Monday.

Earlier this year, the former FBI director said mounting frustrations with Republican lawmakers meant he could no longer “be associated” with the party, despite supporting them for most of his adult life.

— CNBC’s Christina Wilkie contributed to this report.