Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeDemocrats needle GOP on standing up to Trump Democrats needle GOP on standing up to Trump Amash gets standing ovation at first town hall after calling for Trump's impeachment MORE (R-Ariz.) used his formal goodbye speech on Thursday to tout the importance of upholding U.S. institutions and warned that the country's current political climate "is not healthy."

"I believe that we all know well that this is not a normal time, that the threats to our democracy from within and without are real, and none of us can say with confidence how the situation that we now find ourselves in will turn out," Flake said during his floor speech.

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He added that "to say that our politics is not healthy is something of an understatement."

Flake, who is retiring in January, has emerged as one of the President TrumpDonald John TrumpTrump cites tax cuts over judges as having biggest impact of his presidency Trump cites tax cuts over judges as having biggest impact of his presidency Ocasio-Cortez claps back at Trump after he cites her in tweet rejecting impeachment MORE's most vocal GOP critics dating back to the 2016 campaign, when he confronted then-candidate Trump for mocking Sen. John McCainJohn Sidney McCain#JohnMcCainDay trends on Trump's 73rd birthday #JohnMcCainDay trends on Trump's 73rd birthday New poll finds little GOP support for spending cuts to specific federal programs MORE (R-Ariz.) for being captured during the Vietnam War.

He's publicly urged his party to challenge the president's rhetoric, arguing its doing long-term damage both to the Republican Party and the country's democratic institutions, adding on Thursday that they need constant defense to be upheld.

Flake recounted that, while working in Namibia, he read Czechoslovak President Václav Havel's 1990 speech to Congress in which he urged lawmakers to continue to help the Soviet Union, shortly before it dissolved.

"Vladimir Putin would go on to be president and he is president still, and just as he hijacked democracy in his own country, he is determined to do so everywhere. Denial of this reality will not make it any less real. This is something that is staring us in the face, right now, as we are gathered here today," Flake said.

He added that "we are being powerfully reminded just how delicate all of this is, right now."

Flake characterized himself as "filled with gratitude" and "grateful" for serving in the Senate and said he is "optimistic about the future," but also warned that the country is being tested.

He added that Congress has a "solemn obligation" to the international community as an "authoritarian impulse reasserts itself globally."

"Let us recognize from this place here today that the shadow of tyranny is once again enveloping parts of the globe," he said. "And let us recognize as authoritarianism reasserts itself in country after country that we are by no means immune."

More than 15 of Flake's colleagues, including approximately 10 Republican senators, sat in the chamber and listened to Flake's speech.

Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellGOP nervous that border wall fight could prompt year-end shutdown GOP nervous that border wall fight could prompt year-end shutdown Jon Stewart slams McConnell over 9/11 victim fund MORE (R-Ky.) toasted Flake from the Senate floor earlier Thursday, noting his work on earmarks and quipping about him making The Hill's "50 Most Beautiful" list, where he claimed first place in 2013.

"A few years back — now listen to this — he was even named by The Hill newspaper as the No. 1 most beautiful person on Capitol Hill," McConnell said. "Talk about an achievement that few of us could even aspire to."