Rep. Jerry Nadler (D-N.Y.) said Monday that President Obama should fire FBI Director James Comey over the letter he sent to lawmakers last month, less than two weeks before Election Day, about newly discovered emails possibly related to the investigation into Hillary ClintonHillary Diane Rodham ClintonTexas history curriculum to emphasize that slavery played 'central role' in Civil War Election Countdown: Abrams ends fight in Georgia governor's race | Latest on Florida recount | Booker, Harris head to campaign in Mississippi Senate runoff | Why the tax law failed to save the GOP majority Texas education board approves restoring Hillary Clinton in history curriculum MORE's private server.

"The president can fire him for cause and ought to. He violated all the guidelines and put his thumb on the scale of an election. Whether it was decisive or not is a different question," Nadler told CNN's "New Day."

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Comey sent a letter to lawmakers late last month alerting them to possible new evidence in the FBI probe of the private server Clinton used while secretary of State.

One week before the election, Comey sent an additional letter to Congress alerting them that he would not change the earlier conclusion the agency had reached that Clinton's actions did not call for criminal prosecution.

Comey announced in July that he would not recommend charges be brought against the Democratic presidential nominee.

Critics have accused Comey of violating the Justice Department's practice not to take steps that could affect an election.

Nadler said Monday that it was "unforgivable for a police agency to opine publicly about legal conduct."

"To have the policy intervene in an election, which is what happened, is unforgivable, a threat to our democracy, and has got to be stopped and the people who did that have got to be investigated and maybe prosecuted," he added.