President Trump faced harsh bipartisan criticism back home for his Helsinki press conference with Vladimir Putin on Monday, as lawmakers claimed the U.S. president missed a chance to "stand up" to the Russian president on election meddling.

The U.S. president, for his part, called the summit with Putin "deeply productive." After Democrats for days called on him to nix the meeting in the wake of indictments against Russian officers for U.S. campaign hacking, Trump said he would "not make decisions on foreign policy in a futile effort to appease partisan critics."

He cited progress on a range of issues, and said it would be a "good thing" to get along with Russia.

However, the president angered members of both parties by saying both countries share blame for damaged relations and by not firmly standing by U.S. intelligence assessments that Russia meddled in the 2016 elections.

Trump said he has great confidence in the intelligence community, but Putin gave a "strong and powerful" denial. He said he doesn't "see any reason why" Russia would be behind election meddling.

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"There is no question that Russia interfered in our election and continues attempts to undermine democracy here and around the world," House Speaker Paul Ryan, R-Wis., countered.

Others were less reserved in their response.

Sen. John McCain, R-Ariz., who has been out of Washington for months battling brain cancer, issued a blistering statement calling the performance “disgraceful.”

“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, calling the president’s comments at the press conference “a recent low point in the history of the American Presidency.”

Sen. Jeff Flake, R-Ariz., another Republican often critical of the president, also blasted Trump.

“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 tweeted.

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Trump later clarified on Twitter: "As I said today and many times before, 'I have GREAT confidence in MY intelligence people.' However, I also recognize that in order to build a brighter future, we cannot exclusively focus on the past – as the world’s two largest nuclear powers, we must get along!"

Democrats, meanwhile, cranked up the volume on criticism that had already been building for days -- especially after 12 Russians were indicted for allegedly hacking Hillary Clinton campaign and other Democratic groups' emails in 2016.

Former CIA director John Brennan, another frequent critic of Trump, went so far as to effectively accuse the president of treason.

“Donald Trump’s press conference performance in Helsinki rises to & exceeds the threshold of 'high crimes & misdemeanors.' It was nothing short of treasonous. Not only were Trump’s comments imbecilic, he is wholly in the pocket of Putin. Republican Patriots: Where are you???”

House Democratic Leader Nancy Pelosi, D-Calif., said: “President Trump’s weakness in front of Putin was embarrassing, and proves that the Russians have something on the President, personally, financially or politically.”

Senate Democratic Leader Chuck Schumer made similar comments, while calling on Congress to ratchet up sanctions on Russia in response to Monday's events.

"What the president has done is an insult to all Americans," Schumer said.

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Democrats continue to push claims that Russia has 'dirt' on Trump, though the so-called dossier that helped start those theories has not been verified. Monday's press conference only fueled those claims.

Putin, though, was directly asked during the press conference whether he had compromising material on Trump, and dismissed such speculation as “nonsense.”

While the Finland summit between Trump and Putin apparently spanned a range of topics -- from Crimea to missile defense and more -- the press conference itself focused largely on the meddling allegations. Trump used the stage to again condemn Special Counsel Robert Mueller's probe as a "disaster," saying there was “no collusion” with his campaign.

“I didn’t know the president. There was no one to collude with, and there was no collusion with the campaign,” Trump said, suggesting Democrats have used the issue an excuse for losing. “We ran a brilliant campaign, and that’s why I’m president.”

Throughout the joint press conference, Putin emphatically and repeatedly denied meddling in the U.S. election, saying there’s “no evidence.”

In the wake of the comments, Trump's Director of National Intelligence Dan Coats stood by their assessment: "We have been clear in our assessments of Russian meddling in the 2016 election and their ongoing, pervasive efforts to undermine our democracy."

Sen. Elizabeth Warren, D-Mass., considered a potential 2020 presidential candidate, slammed Trump’s comments as “disgraceful.”

“Once again, @realDonaldTrump takes to the international stage to embarrass America, undermine our institutions, weaken our alliances, & embrace a dictator. Russia interfered in our elections & attacked our democracy. Putin must be held accountable – not rewarded. Disgraceful,” Warren tweeted.

Ranking Member of the House Intelligence Committee Adam Schiff, D-Calif., said that Trump’s attack on intelligence agencies would be taken as a “green light” by Putin to “interfere” in the 2018 midterm elections.

Other Republicans, while not as fierce as McCain, also criticized Trump, reminding him that Russia is not considered a “friend” of the U.S.

"Russia is not our friend. Russia attempted to undermine the fundamentals of our democracy, impugn the reliability of the 2016 election, and sow the seeds of discord among Americans. Our intelligence community, including the current one, concluded this, as did the Majority House Intelligence Committee report, as did our fellow Americans who served on grand juries which returned true bills on two separate occasions,” House Oversight Committee Chairman Trey Gowdy, R-S.C., said in a statement, urging administration officials to “communicate to the President it is possible to conclude Russia interfered with our election in 2016 without delegitimizing his electoral success."

Senate Intelligence Chairman Richard Burr, R-N.C., also stressed that Putin “is not our friend and never has been.”