"The enemy of the people was how the president of the United States called the free press in 2017. ... It is a testament to the condition of our democracy that our own president used words infamously spoken by Josef Stalin to describe his enemies," said Flake, who is retiring at the end of his term amid poll numbers that suggested he faced a difficult reelection fight.

He added that the president's comments "should be the source of great shame for us in this body, especially for those of us in the president's party, for they are shameful, repulsive statements, and of course the president has it precisely backwards."

Flake's speech marks one of the strongest Republican rebukes of Trump from the Senate floor. The Arizona senator has

emerged as one of the loudest Republican critics of Trump since he started his presidential campaign in 2015. The feuds with Trump appear to have hurt Flake with GOP primary voters in his state, however.

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GOP lawmakers, while frequently caught off guard by Trump's statements, have also argued that reporters should focus on what the president does, not what he says.

"When a figure in power reflexively calls any press that doesn't suit him fake news, it is that person who should be the figure of suspicion, not the press," he said.

Flake's remarks come as Trump has said he will give out a "Fake News Award" this week.

Flake called the award a "spectacle," adding that Congress cannot continue to give "silent acquiescence" to Trump's rhetoric.

"An American president who cannot take criticism, who must constantly deflect and distort and distract, who must find someone else to blame is charting a very dangerous path, and a Congress that fails to act as a check on the president adds to that danger," he said.

"I rise today to thank my colleague, Senator Flake, for his words and to join him in standing up for the First Amendment," Klobuchar said after the speech.

Durbin added that "we are facing an attack on an American institution, an attack on our freedom of press."

One of the Republicans hoping to succeed Flake, however, ripped him for his criticism of Trump.

"Jeff Flake’s comparison of President Trump to the brutal dictator Joseph Stalin on the floor of the United States Senate was appalling and an embarrassment to the state of Arizona," Kelly Ward said in a statement.

"Arizona voters deserve representation in the U.S. Senate that, regardless of political differences, will never engage in this type of troubling rhetoric," Ward said. "I call on all the candidates in the race to replace him in the Senate to join me in publicly condemning his remark."

White House press secretary Sarah Huckabee Sanders also criticized Flake over the speech.

"I found it quite interesting that he is coming out to attack this president considering he is one who was recently defending an actually oppressive regime," Sanders said during a White House press briefing later in the day. "He went to Cuba a few weeks ago and served as a mouthpiece for the oppressive Cuban government. He is not criticizing the president because he is against oppression, he is criticizing the president because he has terrible poll numbers and he is, I think, looking for some attention."

"To be very clear, to call the Russian matter a hoax, as President Trump has done so many times, is a falsehood," Flake added.

Updated: 1:50 PM EST.