Donald Trump returned late on Monday from his European tour to face ire in Washington, where US intelligence officials and senior Republicans were denouncing the president as “shameful” and “disgraceful” after he refused to challenge Russian leader Vladimir Putin over interference in American elections.

Republican Senator John McCain said Trump's seeming acceptance of Putin's denial was a historical “low point” for the US presidency and the Helsinki summit between the two leaders a “tragic mistake.”

“Today's press conference in Helsinki was one of the most disgraceful performances by an American president in memory. The damage inflicted by President Trump's naivete, egotism, false equivalence, and sympathy for autocrats is difficult to calculate,” McCain said in a blistering statement.

“No prior president has ever abased himself more abjectly before a tyrant.”

Taking direct issue with the president who appointed him, Director of National Intelligence Dan Coats said US spy agencies have been “clear” and “fact-based” in their assessment that Moscow interfered in the presidential race two years ago — an assessment that Trump refused to endorse in Helsinki.

Coats added that Russia remains behind “ongoing, pervasive efforts to undermine our democracy.”

Denial comes after 12 Russians indicted

Trump stunned US political allies and foes alike with his answer to a question about Russian hacking and interference in the 2016 election which saw him defeat Democrat Hillary Clinton.

Putin “just said it is not Russia. I will say this: I don't see any reason why it would be,” Trump said. That came three days after the US Justice Department indicted 12 Russians for hacking Democratic Party computers, the latest in a series of actions taken by the US government since late 2016 in retribution for what intelligence agencies say was a broad plan to support Trump's election campaign directed by Putin himself.

Yet Trump appeared to take Putin's word in dismissing that conclusion. “I have great confidence in my intelligence people. But I will tell you that President Putin was extremely strong and powerful in his denial today.”

Trump also appeared to embrace Putin's offer to have Russian investigators work together with US prosecutors on the case of the 12 just indicted. “I think that's an incredible offer,” he added.

Astonished Republicans and Democrats uniformly condemned Trump, with harsh criticism coming even from hosts on Fox News — a network normally friendly to the president.

“The president must appreciate that Russia is not our ally,” said Republican House Speaker Paul Ryan. “There is no moral equivalence between the United States and Russia, which remains hostile to our most basic values and ideals,” he said.

Senior Republican Senator Lindsey Graham said Trump's answer on meddling “will be seen by Russia as a sign of weakness.”

Bent on forging a personal bond with the Kremlin chief, Trump headed into the summit blaming the “stupidity” of his predecessors for plunging ties to their present low.

“This is shameful,” said Senator Jeff Flake, a fellow Republican and staunch critic of the president. “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.”

'Green light to interfere'

The language used by Democrats was much harsher, including accusations of “treason.”

“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,” said Chuck Schumer, the senior Democrat in the Senate.

Democratic California Representative Jimmy Gomez charged: “To side with Putin over US intelligence is disgusting; to fail to defend the US is on the verge of treason.”

Congressman Adam Schiff, the senior Democrat on the House Intelligence Committee, said Trump had given Putin “a green light to interfere in 2018.”

Democratic Senator Chris Murphy was blunter: “This entire trip has just been one giant middle finger from President Trump to his own country. Just jaw dropping,” he wrote on Twitter.

Coats' statement was seen as an uncommonly brusque pushback by the US intelligence community against the White House.

Retired spy chiefs were more direct. Coat's predecessor, James Clapper, called Trump's acquiescence to Putin “an incredible capitulation,” while former CIA chief John Brennan labelled it “nothing short of treasonous.“