WASHINGTON, DC -- Senators from both sides of the aisle expressed surprise and concern after president Donald Trump fired FBI director James Comey late Tuesday afternoon.

Top Senate Democrat Chuck Schumer said people will suspect a cover-up by the president as the FBI investigates alleged Russian interference in the presidential election and whether there was collusion by the Trump campaign.

Schumer and other Democrats say an independent prosecutor, removed from the U.S. Justice Department, is now essential for the investigation's integrity.

MORE: President Donald Trump fires FBI Director James Comey

"The first question the Administration has to answer is why now?," Schumer said. "If the administration had objections to the way Director Comey handled the Clinton investigation, they had those objections the minute the president got into office. But they didn't fire him then. Why did it happen today?

"We know the House has been investigating Russian interference in our elections that benefitted the Trump campaign," Schumer said. "We know the Senate is investigating. We know the FBI has been looking into whether the Trump campaign colluded with the Russians, a very serious offense. Were these investigations getting too close to home for the President?"

Even several Republican senators issued statements expressing concern.

U.S. Sen. Richard Burr said he was "troubled by the timing and reasoning" of the dismissal.

"I regret that that took place," said U.S. Sen. John McCain of Arizona. "The president does have that authority so I respect that."

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