On a trip in which Donald Trump dumbfounded allies and his usual critics in the Democratic Party with comments concerning the European Union and British leaders, the U.S. president ended with a news conference performance at his first head-to-head summit with Russian President Vladimir Putin that had even some Republicans shaking their heads.

Democrats had called on Trump to scrap the meeting in Finland and not give Putin legitimacy on the heels of the announcement of new indictments in the special counsel probe investigating Russian interference into the 2016 presidential election and Russian contacts with members of Trump's campaign team.

When asked directly on Monday if he held Russia "accountable for anything," Trump said he held "both countries responsible," echoing language he used after hostilities broke out last year when white nationalists rallied in Virginia.

"I think the United States has been foolish, I think we've all been foolish. We should have had this dialogue a long time ago," said Trump, who has twice previously met with Putin on the sidelines

The comments prompted Sen. Ben Sasse, a Nebraska Republican, to release a statement characterizing it "bizarre and flat out wrong."

Watch as Trump blames both the U.S. and Russia for frosty relations between the countries.

'I think that the United States has been foolish,' U.S. president says at Helsinki news conference 2:00

Trump also again assailed the investigation being led by former FBI director Robert Mueller into Russian interference in the 2016 election, calling it a "disaster for our country," and seemingly expressed skepticism over the findings of his own intelligence agencies.

Mark Warner, the top ranking Democrat on the Senate's foreign intelligence committee, said it was a "disgrace" Trump appeared to side with Putin over his own intelligence agencies. To Senate minority leader Chuck Schumer, it was something not seen "in the entire history of our country."

For the President to side with Putin over his own intelligence officials and blame the United States for Russia’s attack on our democracy is a complete disgrace. —@MarkWarner

In the entire history of our country, Americans have never seen a president of the United States support an American adversary the way <a href="https://twitter.com/realDonaldTrump?ref_src=twsrc%5Etfw">@realDonaldTrump</a> has supported President Putin. —@SenSchumer

When asked point blank whether he'd challenge Putin on the subject of Russia interference, Trump avoided the question and pivoted to concerns he had about the investigation into Hillary Clinton's use of a private email server when she was secretary of state.

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Trump said he clearly "beat Hillary Clinton easily," referring to the 2016 election results in which he won the electoral college in key states of Michigan, Wisconsin and Pennsylvania by a total of some 77,000 votes, losing the popular vote by some three million.

Former CIA director John Brennan, who has been among the most vocal of past officials in his criticism of the president, was unsparing.

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??? —@JohnBrennan

Brennan, in a subsequent television interview with MSNBC, also said, "This, I think, rises to the point of good American patriots resigning in objection to that performance," referring to Secretary of State Mike Pompeo, chief of staff John Kelly and national security adviser John Bolton by name.

Dan Coats, the director of national intelligence, has continually sounded the alarm that Russia will look to also interfere with the U.S. midterm elections in 2018. Coats was referred to by Trump at the Helsinki news conference, and then essentially dismissed.

Statement from DNI Coats <a href="https://t.co/4nb43vQ7ID">https://t.co/4nb43vQ7ID</a> <a href="https://t.co/OCJE0MqW1j">pic.twitter.com/OCJE0MqW1j</a> —@ODNIgov

Coats's office released a statement three hours after the meeting stressing that Russian efforts to meddle were "pervasive," and that it would continue to provide "unvarnished and objective intelligence."

The flurry of response came after an event in Helsinki on Monday, when Trump said Putin strongly denied meddling in the 2016 election.

"I have President Putin — he just said it's not Russia," Trump said. "I will say this: I don't see any reason why it would be."

Watch as Trump deflects a direct question about Russian election interference.

Blames Democrats and Hillary Clinton, and says he believes Vladimir Putin's denial of any wrongdoing 4:41

Trump issued a tweet later Monday that appeared to respond to some of the criticism, saying, "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!"

He later sent another tweet saying, "a productive dialogue is not only good for the United States and good for Russia, but it is good for the world.

Vice-President Mike Pence stood alongside his boss, saying the meeting was constructive. According to Pence, the meeting showed Americans and the world that Trump "will always put the prosperity and security of America first."

'I am done with him'

Pence's view stood apart from many of Trump's rivals, but what was striking about the snap reaction to Monday's assorted comments from Trump was the disappointment and even scorn from the Republican side of the aisle.

Senate Majority Leader Mitch McConnell didn't answer when asked if he was disappointed in the president's remarks, but he did say that the Russians "are not our friends." And he said he "entirely" agrees with intelligence agencies' assessment that Russians meddled in the election.

Radio talk show host Joe Walsh, a self-described Tea Party conservative who served a term earlier this decade as a U.S. congressman, said on social media, "I am done with him." He implored fellow Republicans to speak out in a subsequent Twitter post.

This press conference is an absolute disgrace. Trump won't even side with America.<br><br>What Trump did today was commit treason. He cannot be supported anymore. He is a clear & present danger to America. Republicans can no longer be quiet.<br><br>I won't be quiet. I am done with him. —@WalshFreedom

Senators Jeff Flake, and to a lesser extent, Lindsey Graham, have been among a small group of Republicans in Congress who have occasionally criticized perceived lapses in judgment by Trump since his inauguration last year.

Arizona's Flake, who has felt free to speak his mind since announcing he won't run for another term, deemed Trump's comments on Monday "shameful," with Graham of South Carolina admitting it will be perceived as "a sign of weakness."

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. —@JeffFlake

Missed opportunity by President Trump to firmly hold Russia accountable for 2016 meddling and deliver a strong warning regarding future elections. <br><br>This answer by President Trump will be seen by Russia as a sign of weakness and create far more problems than it solves. (1/3) —@LindseyGrahamSC

Today’s press conference in <a href="https://twitter.com/hashtag/Helsinki?src=hash&ref_src=twsrc%5Etfw">#Helsinki</a> was one of the most disgraceful performances by an American president in memory.<br><br>My full statement on the <a href="https://twitter.com/hashtag/HelsinkiSummit?src=hash&ref_src=twsrc%5Etfw">#HelsinkiSummit</a>: <a href="https://t.co/lApjctZyZl">https://t.co/lApjctZyZl</a> —@SenJohnMcCain

The most consistent critic of Trump in the upper chamber has been Flake's fellow Arizonan John McCain, who last year helped scuttle the president's attempt to get rid of the Affordable Health Care Act, known as Obamacare.

"No prior president has ever abased himself more abjectly before a tyrant," said McCain in a statement.

While in Helsinki, Putin suggested that Moscow and Washington could jointly conduct an investigation into allegations of election meddling by Russia — but in return, he would expect the U.S. to co-operate in the Russian probe against Bill Browder, a U.S-born British investor charged with financial crimes in Russia.

Browder, an outspoken Putin critic, spoke to CBC News on Monday from an undisclosed location. In 2005, Browder was declared an enemy of the state by Moscow for his part in exposing corruption in Russia.

Browder, an outspoken critic of the Russian president, says 'Vladimir Putin is a global menace' and the summit should never have happened. 9:21

Browder said Putin has become "obsessed" with arresting him because he "put [Putin's] money and the money of his criminal cronies at risk under the Magnitsky Act" — a series of U.S. laws that target the holdings of corrupt foreign officials.

He also called Putin a "global menace."

"He's playing Trump and the United States like a fiddle right now," Browder told CNBC on Monday.

House Speaker Paul Ryan chided the president for false equivalency in his answer about accountability.

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

Trump has sometimes received completely praiseworthy coverage from Fox News following big moments on the global stage, but he did not earn a total pass on the right-wing network. Fox News anchor Bret Baier called the news conference "surreal," while Fox Business veteran Neil Cavuto said the president's inability to take a strong stance concerning the consequences of future cyberattacks directed at the U.S. "made it disgusting."

"It's not a left or right thing, it's just wrong," said Cavuto, who was incredulous Trump didn't even offer "a mild criticism" of the Russian leader.

No negotiation is worth throwing your own people and country under the bus. —@HuntsmanAbby

Neil Cavuto of Fox Business calls Trump's press conference "disgusting", "That sets us back a lot." <a href="https://t.co/R2ZIjyFyPR">pic.twitter.com/R2ZIjyFyPR</a> —@axios

Abby Huntsman, another Fox on-air personality, opined, "no negotiation is worth throwing your own people and country under the bus."

Huntsman, it should be noted, is the daughter of Trump's ambassador to Russia, Jon Huntsman, who was in the room on Monday in Helsinki.

Ahead of the summit, Trump said he would press Putin on the issue of Russian interference in the election but that he didn't expect a "Perry Mason" moment to result.

Melania Trump and U.S. Secretary of State Mike Pompeo look on during the news conference in Helsinki. Former CIA director John Brennan said top officials like Pompeo should really consider whether they can continue serving the president. (Kevin Lamarque/Reuters)

Trump's reluctance to go as hard on the Russian leader while breaching standard public protocol with allies like Britain's Theresa May, Germany's Angela Merkel and Canada's Justin Trudeau, has raised the spectre for some critics that the former KGB and FSB intelligence officer Putin has compromising information on the president.

Putin insisted the claims were "sheer nonsense."

"Do you really believe that we try to shadow every businessman?" he said.

Watch the full Trump-Putin news conference below.