James Comey has urged “all who believe in this country’s values” to vote for the Democrats in the upcoming midterm elections.

The former FBI director, who has been a Republican for much of his life, said the Republican-led Congress “has proven incapable of fulfilling the Founders’ design.”

In a tweet, Mr Comey said: “This Republican Congress has proven incapable of fulfilling the Founders’ design that ‘Ambition must ... counteract ambition.’”

His message referred to the need for Congress to provide checks and balances on presidential power.

He added: ”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.”

Mr Comey, who was fired from his job as FBI director by Donald Trump last year, recently said he no longer considers himself a Republican.

On Monday, after the US president’s press conference with his Russian counterpart, Vladimir Putin, Mr Comey tweeted: “This was the day an American president stood on foreign soil next to a murderous lying thug and refused to back his own country.”