President Donald Trump was swiftly rebuked by lawmakers, TV anchors and pundits across the political spectrum Monday after his joint news conference in Finland with Russian President Vladimir Putin.

Sen. John McCain, R-Ariz., who has criticized the president's posture toward Russia in the past, called it "one of the most disgraceful performances by an American president in memory."

The summit, which took place between Trump and Putin at Finland's presidential palace Monday in Helsinki, was a "tragic mistake," McCain said. But dismissing the news conference that followed as a "pathetic rout" of a political novice is too generous, he added.

"President Trump proved not only unable, but unwilling to stand up to Putin. He and Putin seemed to be speaking from the same script as the president made a conscious choice to defend a tyrant against the fair questions of a free press, and to grant Putin an uncontested platform to spew propaganda and lies to the world," McCain said.

Former CIA director John Brennan, a frequent Trump critic and an national security analyst for NBC News and MSNBC, called Trump's performance "nothing short of treasonous."

Trump met with Putin one-on-one for more than two hours and in a session with aides present. In the joint appearance after their summit, Trump downplayed the assessment of the U.S. intelligence community that Moscow mounted an effort to help him win the presidency in 2016, blasted the American news media, bashed the FBI and the special counsel investigation into Russian election meddling, and suggested that Putin was more credible than his own director of national intelligence, who has accused Russia of mounting an "unprecedented influence campaign" in 2016.

"[Putin] just said it's not Russia," Trump said. "I will say this: I don’t see any reason why it would be."

His remarks were met with an outpouring of condemnation from Republicans, Democrats, and even Fox TV hosts, who accused the president of undermining his country's intelligence community while embracing an adversary.

GOP to Trump: 'Putin is not our friend'

Former GOP House Speaker Newt Gingrich, a Trump confidant, called the president's comments "the most serious mistake of his presidency."

"President Trump must clarify his statements in Helsinki on our intelligence system and Putin," Gingrich tweeted. "It is the most serious mistake of his presidency and must be corrected—immediately."

Retiring Republican Sen. Jeff Flake of Arizona, a frequent critic of the president, said Trump was wrong to hold the U.S. partly responsible for the deterioration of the relationship between the two countries.

"I never thought I would see the day when our American President would stand on the stage with the Russian President and place blame on the United States for Russian aggression. This is shameful," Flake said.

House Speaker Paul Ryan, R-Wisc., who rarely criticizes Trump publicly, contradicted Trump's equivocations about Moscow's election meddling and said "the president must appreciate that Russia is not our ally."

"There is no question that Russia interfered in our election and continues attempts to undermine democracy here and around the world," Ryan said in a statement.

"There is no moral equivalence between the United States and Russia, which remains hostile to our most basic values and ideals. The United States must be focused on holding Russia accountable and putting an end to its vile attacks on democracy," Ryan added.

"A person can be in favor of improving relations with Russia, in favor of meeting with Putin, and still think something is not right here," tweeted Rep. Justin Amash, R-Mich.

Republican Sen. Bob Corker, chairman of Senate Foreign Relations Committee, said he didn't think it was "a good moment for our country.

"Actually, sometimes the president cares more about how a leader treats him personally than forcefully getting out there and pushing against things that we know have harmed our nation, and I thought that's what we all experienced today," Corker said.

Sen. Richard Burr, R-N.C., the chairman of the Senate Intelligence Committee, pushed back against Putin’s assurance at the Helsinki summit that his country did not meddle in the election, calling it "a lie" and adding that it should be recognized as one by the president.

"Vladimir Putin is not our friend and never has been. Nor does he want to be our friend. His regime’s actions prove it. We must make clear that the United States will not tolerate hostile Russian activities against us or our allies," Burr said in a statement.

Mitt Romney, the former Republican presidential candidate now running for U.S. Senate in Utah, called Trump's "decision to side with Putin" over the conclusions of American intelligence agencies "disgraceful and detrimental to our democratic principles."

Pundits and conservative media: Trump threw his country 'under the bus'

Fox News and Fox Business personalities found themselves at odds with Trump, as well.

Abby Huntsman, a Fox News reporter and daughter of U.S. Ambassador to Russia Jon Huntsman, excoriated Trump in a tweet, saying "no negotiation is worth throwing your own people and country under the bus."

Fox Business Network host Neil Cavuto also blasted the president for appearing to believe Putin over the assessments of the U.S. intelligence community that Russia interfered in the election, calling Trump's performance "disgusting."

"I'm sorry, it's the only way I feel. It's not a right or left thing to me, it's just wrong," Cavuto said.

Guy Benson, a conservative Fox News contributor, called Monday "easily one of his worst days as president."

Thomas Pickering, who served as the ambassador to Russia under President Clinton, said in an interview with MSNBC's "Andrea Mitchell Reports" that Trump's suggestion that Russia did not interfere in the election is "a breathtaking denial of something that is so obviously true."

It epitomizes Trump’s penchant for self-promotion over "defending the national interest of the United States," he said.

Former FBI Director James Comey, who was fired by Trump last year, said Trump declined to support his own country.

"This was the day an American president stood on foreign soil next to a murderous lying thug and refused to back his own country," Comey tweeted. "Patriots need to stand up and reject the behavior of this president."

Democrats: Trump's behavior was weak, embarrassing, un-American

Former Vice President Joe Biden pilloried the president for his embrace of Putin after attacking U.S. allies during his European trip last week.

"Today our President had the chance to confront an adversary who has attacked — and continues to attack — our democracy and our allies. He could have stood up for American interests and values. He chose not to," Biden said. "Today’s press conference was beneath the dignity of the Office of the President."

Trump's performance was "the most astonishing display of weakness and submission that I have ever seen from an American President," Rep. Don Beyer, D-Va., said in a statement.

Rep. Adam Schiff, D-Calif., the ranking member of the House Intelligence Committee, called the president’s remarks "cowardly and shameful" in a tweet and suggested Trump's actions will invite more Russian meddling in the midterms.

House Minority Leader Nancy Pelosi, D-Calif., called Trump's performance an embarrassment. She also suggested, without evidence, the Russians may have damaging information about the president.

“President Trump's weakness in front of Putin was embarrassing, and proves that the Russians have something on the President, personally, financially or politically," she said in a statement.

Senate Minority Leader Chuck Schumer, D-N.Y., called Trump's unwillingness to push back against Putin more strongly "thoughtless, dangerous and weak."

"The president is putting himself over our country," he said. "Millions of Americans will continue to wonder if the only possible explanation for this dangerous behavior is the possibility that President Putin holds damaging information over President Trump."