The Republican firebrand sided with the Kremlin and seemed to accept Putin’s denial of US election meddling during a joint press conference on Monday.
And the President gave no criticism of Russia or the cyber-hacking of the 2016 election US intelligence agencies say the leader of the Eastern superstate co-ordinated.
Former CIA director John Brennan slammed Trump’s neglect of his own intelligence services.
He tweeted: “Not only were Trump’s comments imbecilic, he is wholly in the pocket of Putin.
“It was nothing short of treasonous.
“Donald Trump’s press conference performance in Helsinki rises to and exceeds the threshold of ‘high crimes and misdemeanours’.”
One of Trump’s own Senators accused the President of making America look like “a pushover” by refusing to stand up to Putin.
Bob Corker, the Senator for Tennessee, told broadcaster CNN: “The President’s comments made us look as a nation more like a pushover and I was disappointed in that.
“When he had the opportunity to defend our intelligence agencies who work for him, I was very disappointed and saddened with the equivalency that he gave between them and what Putin was saying.”
Republican heavyweights also labelled Trump’s comments “disgraceful”.
Mitt Romney, former Republican presidential nominee, said Trump had acted against America’s democratic principles.
He tweeted: “President Trump’s decision to side with Putin over American intelligence agencies is disgraceful and detrimental to our democratic principles.
“Russia remains our number one geopolitical adversary.
“A moral equivalence between the United States and Russia not only defies reason and history, it undermines our national integrity and impairs our global credibility.”
John McCain called the whole meeting a “tragic mistake”.
The Arizona Senator said: “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 naivety, egotism, false equivalence, and sympathy for autocrats is difficult to calculate.
“But it is clear that the summit in Helsinki was a tragic mistake.”