SHAMEFUL, embarrassing, imbecilic – voices from across US politics have hammered home their criticism of Donald Trump following landmark talks with Vladimir Putin.

The American leader stood tall behind the lectern in Finland, drawing himself up to full height next to his shorter Russian counterpart during a highly scrutinised press conference.

But his message failed to dominate as critics hit out at the soft line taken on key issues, including that on possible interference in the US presidential election.

WATCH: CNN news anchor calls Trump press conference 'disgraceful'

READ MORE: Donald Trump jets out of Scotland after weekend of UK protests

During the session, Trump slammed the FBI for its investigation, describing it as a "disaster" for America, and insisting there had been "no collusion" in his defeat of Democratic rival Hillary Clinton in 2016.

Trump said the pair had spent "a great deal of time" talking about the issue, and that Putin had an "interesting idea", but failed to give further details.

But an outspoken John Brennan, former director of the CIA, said Trump's performance had been "nothing short of treasonous".

He tweeted: "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?"

Republican senator Jeff Flake stated: "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."

And Democrat leader Nancy Pelosi said: "Just several days ago, 12 Russians were indicted for attacking our democracy. Today, America's so-called leader embarrassingly failed to stand up to the person who spearheaded the attack.

"Seriously, what does Putin have on Trump that's he's so afraid?"

That question was posed to Putin during the Helsinki press event, with the Kremlin leader laughing in response.

It has long been suggested that Russian security forces hold compromising material on the hotel magnate, but no evidence has surfaced and the claim has been strongly refuted by Trump's side.

Putin said: "I did hear these rumours. When President Trump visited Moscow back then, I didn't even know he was in Moscow."

But former White House press secretary Ari Fleischer commented: "I continue to believe there was no collusion between the Trump campaign and Russia. But when Trump so easily and naively accepts Putin’s line about not being involved, I can understand why D[emocrat]s think Putin must have the goods on him."

And Michael Steele, former chair of the Republican national committee, had his own take on the dynamics between the two men, using the terminology deployed by the intelligence community to describe sources and agency operatives.

He tweeted: “That's how a press conference sounds when an asset stands next to his handler.”

South Carolina senator Lindsey Graham, who is also from Trump's party, commented that it had been a "bad day for the US", adding: "Must be fixed."

The politician – who suggested that Trump check his football gift from Putin "for listening devices and never allow it in the White House" – stated: "Meddling & collusion are NOT the same thing. Russia did meddle in 2016 election & are trying it again. I’ve seen no evidence of collusion, plenty evidence of Russian meddling."