Senate Minority Leader Chuck Schumer said he warned President Trump in a phone call Tuesday not to fire FBI Director James Comey, something he said could be viewed as a "cover-up" of a probe into alleged Russian connections with the Trump campaign.

"I told the president, 'with all due respect, you are making a big mistake,'" Schumer, D-N.Y., said at an evening press conference in the Capitol. "The first question that he has to answer is, why now?"

Schumer is demanding the Justice Department appoint a special prosecutor to examine alleged Russian connections with the Trump campaign.

Schumer suggested Comey, who was investigating the matter, was fired for political reasons by Trump.

"We know the FBI has been looking into whether the Trump campaign colluded with the Russians," Schumer said.

Congress is also investigating whether there was any Trump campaign collusion with the Russians.

"Were these investigations hitting too close to home for the president?" Schumer said.

Schumer said when warned Trump that firing Comey would be a mistake, Trump "didn't really answer."

Schumer also questioned why Attorney General Jeff Sessions played a role in the decision to fire Comey, given that Sessions, an early Trump supporter, had recused himself from any probe of the Russian connection to the Trump campaign. Rod Rosenstein, the deputy attorney general, is in charge of the probe.

The New York Democrat said if Rosenstein does not appoint a special prosecutor, "every American will rightly suspect that the decision to fire Director Comey was part of a coverup."