By Clare Foran, CNN

(CNN) -- In his farewell speech to Congress, departing GOP Senator Jeff Flake issued a warning that "the threats to our democracy from within and without are real" and that the country is experiencing a "moment of political dysfunction and upheaval."

Flake, a frequent conservative critic of President Donald Trump, made the remarks in an address on the Senate floor. The Arizona Republican is retiring at the end of his current term and leaving the Senate.

During the speech, Flake argued that democracy is at risk of being undermined not just in the United States, but also abroad in the face of what he described as a resurgent "authoritarian impulse."

"As the authoritarian impulse reasserts itself globally and global commitment to democracy seems now to be on somewhat shaky ground, I have been thinking a lot recently about the American commitment to democracy, where it comes from and how if the circumstances were right, it might slip away," he said.

Flake later said, "The shadow of tyranny is once again enveloping parts of the globe and let us recognize as authoritarianism reasserts itself in country after country, that we are by no means immune."

"The road to democracy is not irreversible," he said, adding, "not in America, not anywhere."

Flake stated that it would be an "understatement" to "say that our politics is not healthy," and that he believes "we all know well that this is not a normal time and that the threats to our democracy from within and without are real."

He added, "We are of course testing the institution of American liberty in ways that none of us ever imagined we would -- and in ways that we probably never should again."

In describing what he believes are threats to democracy, Flake called out Russian President Vladimir Putin by name, setting up a contrast with Trump, who has been repeatedly unwilling to criticize Putin's actions.

"Just as he hijacked democracy in his own country, he is determined to do so everywhere," Flake said of Putin. "Denial of this reality will not make it any less real."

Flake argued in his speech that work must be done to protect democracy and democratic institutions.

"As we in America during this moment of political dysfunction and upheaval contemplate the hard-won conventions and norms of democracy, we must continually remind ourselves that none of this is permanent: that it must be fought for continually."

Despite outlining those concerns, Flake said that he is departing the Senate with a sense of optimism about what lays ahead and grateful for the experience he had in Congress.

"I leave here grateful and optimistic," he said, saying that it has been a privilege to "serve the state and the country that I love so well."

He added that while he believes "serious challenges lay ahead," the US has "confronted and survived more daunting challenges than we now face."

"Ours is a durable, resilient system of government designed to withstand the foibles of those who sometimes occupy these halls, including yours truly," he added.