Senator Lindsey Graham, a senior Republican and member of the Senate Armed Services Committee, on Monday said of Trump’s performance at a press conference with Putin following their summit in Helsinki:

“Missed opportunity by President Trump to firmly hold Russia accountable for 2016 meddling and deliver a strong warning regarding future elections. This answer by President Trump will be seen by Russia as a sign of weakness and create far more problems than it solves.”

Republican Trump, standing alongside Putin in front of reporters, said he saw no reason to believe Russia had hacked the 2016 U.S. election to help him win and that Putin “was extremely strong and powerful in his denial today.”

Senate Democratic Leader Charles Schumer said Trump’s approach in Helsinki was unprecedented for a leader of the United States.

“For the president of the United States to side with President Putin against American law enforcement, American defence officials, and American intelligence agencies is thoughtless, dangerous, and weak,” Schumer said.

Another Republican senator, Jeff Flake, on Twitter called Trump’s words “shameful.”

“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 wrote.

Trump also said that he holds both the United States and Russia responsible for years of strained relations, which he said he is now trying to improve. Washington imposed sanctions on Moscow after Russia’s 2014 annexation of Crimea from Ukraine as well as for cyber attacks on the American electoral process.

Republican Representative Justin Amash, an outspoken conservative, said on Twitter: “A person can be in favour of improving relations with Russia, in favour of meeting with Putin, and still think something is not right here.”

"I hold both countries responsible," Trump said in response to a question from the American press about Russia's interference. "I think that the United States has been foolish. We've all been foolish. We're all to blame." He went on to deride the FBI, special counsel Robert Mueller's investigation, the US intelligence community,

I mean, WHAT? W-H-A-T?

"Donald Trump's press conference performance in Helsinki rises to & exceeds the threshold of 'high crimes & misdemeanors,'" tweeted former CIA Director John Brennan. "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???"