Hours after FBI director James Comey’s damning testimony into the Trump campaign’s links to Russia, commentators have been moved to call Monday the darkest day of the young presidency.

The revelations followed Mr Trump’s worst polling numbers since taking office.

CNN political analyst Gloria Borger said in a segment on the network that the news marked “the worst and most perilous day of Donald Trump’s young presidency” and that it left “a cloud hanging over the Trump administration”.

“In this hearing over the last bunch of hours, we have seen the director of the FBI rebut Donald Trump directly.

“They are going to have a hard time figuring out how to handle it,” Borger said.

NBC News called Mr Comey’s testimony as a “political gut-punch” Mr Trump, adding “the news possibly could get worse for the president in the days and weeks ahead”.

And political news website politico.com said the news had knocked the “White House on its heels” and had the administration scrambling to contain the fallout.

It was another blow for the Trump presidency after a Gallup poll of 1500 people released at the weekend showed Mr Trump’s lowest approval ratings since he assumed office.

Mr Trump’s approval rating has slumped to 37 per cent, down from 45 per cent just one week earlier, while those who disapprove of the President’s performance is 58 per cent.

Mr Comey confirmed the investigation into the links at a congressional intelligence committee hearing early on Tuesday (AEDT), saying the FBI had evidence showing Russia tried to influence the US election to benefit Mr Trump.

The ongoing investigation was examining whether those Russian efforts were aided, co-ordinated or assisted by Mr Trump’s campaign team.

“I have been authorised by the Department of Justice to confirm that the FBI, as part of our counterintelligence mission, is investigating the Russian government’s efforts to interfere in the 2016 presidential election,” Mr Comey said.

“And that includes investigating the nature of any links between individuals associated with the Trump campaign and the Russian government and whether there was any coordination between the campaign and Russia’s efforts.”

In a double blow to the White House, Mr Comey used the same appearance to debunk the President’s claim he was wiretapped by former president Barack Obama.

The allegation first emerged earlier this month during a presidential twitter tirade that offered no evidence to support it.

Mr Comey told the committee: “I have no information that supports those tweets.”

Mr Trump fired off several tweets during the committee’s hearing, with congressmen reading the tweets to the witnesses to test their veracity.

The Democrats made up and pushed the Russian story as an excuse for running a terrible campaign. Big advantage in Electoral College & lost!

— Donald J. Trump (@realDonaldTrump) March 20, 2017

Rumours and speculation about Mr Trump’s links to Russia have been swirling since he announced he was running for the US Presidency.

These include Mr Trump’s personal involvement and business dealings with Russia, his fondness for Russian President Vladimir Putin and communication between Mr Trump’s close allies and influential Russian figures.

In February 2017, just days after Mr Trump became President, his national security advisor Michael Flynn was sacked for not disclosing conversations with Russian officials during the election campaign.

Then in March, Mr Trump’s Attorney-General, Senator Jeff Sessions, was found to have held conversations with Russia’s ambassador to the US during the campaign and administration handover period.

Mr Sessions did not disclose these conversations and recused himself from any Justice Department-headed investigations into Mr Trump’s links to Russia as a result.

James Comey has confirmed the FBI is investigating Russian efforts to interfere in the 2016 presidential election: pic.twitter.com/EvlzdOZ9qn

— Vox (@voxdotcom) March 20, 2017

“I think that was a fairly easy judgment for the community,” Mr Comey said on Tuesday morning.

“Putin hated [Democratic Presidential nominee] Secretary Clinton so much that the flip side of that coin was he had a clear preference for the person running against the person he hated so much.”

“We will never know whether the Russian intervention was determinative in such a close election. … What does matter is this: The Russians successfully meddled in our democracy and our intelligence agencies have concluded they will do so again.”

Nothing to see here:  Sean Spicer

Mr Comey’s denial of Mr Trump’s claims that former President Barack Obama tapped the billionaire’s phones during the campaign was categorical.

“With respect to the president’s tweets about alleged wiretapping directed at him by the prior administration, I have no information that supports those tweets, and we have looked carefully inside the FBI,” he said.

Mr Trump denies he has anything to do with Russia, despite claims otherwise. Photo: PA Wire

“The Department of Justice has asked me to share with you that the answer is the same for the Department of Justice and all its components.”

Mr Trump’s spokesperson Sean Spicer seemed to not accept Mr Comey’s testimony following the congressional hearing.

“For everyone looking for a conclusion today there is a lot more that needs to be discussed and looked at before we can jump to a conclusion,” Mr Spicer said.

“There is this media narrative about collusion that continues to exist and yet everybody who has been briefed … have all said that nothing that they’ve seen makes them believe there was any collusion.

“There is a difference between talking about an investigation into the 2016 election … and any evidence of collusion.”