After claims and counterclaims about international espionage and spying closer to home, it was a much-anticipated appearance before the House Intelligence Committee.
And FBI director James Comey did not disappoint, offering some unprecedented revelations about the workings of the agency.
He has confirmed an investigation is underway into Russian government meddling in the United States presidential race.
"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. As with any counterintelligence investigation, this will also include an assessment of whether any crimes were committed. Because it is an open, ongoing investigation and is classified, I cannot say more about what we are doing and whose conduct we are examining."
And in another blow to President Trump, James Comey says there is no evidence backing his allegations that predecessor Barack Obama ordered wire-tapping on him.
Mr Trump has alleged Mr Obama ordered wire taps on the Trump Tower offices in New York in the lead-up to the November election, but Mr Comey has cast doubt on it.
"I have no information that supports those tweets, and we have looked carefully inside the FBI. 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. The department has no information that supports those tweets."
In a media briefing, White House spokesman Sean Spicer was asked if the President would apologise to Barack Obama after Mr Comey's testimony.
(Reporter:) "So is the President prepared to withdraw that accusation and apologise to (President Obama)?"
(Spicer:) "No, we started a hearing, it's still ongoing, and then, as Chairman (Devin) Nunes mentioned, this is one in a series of hearings that will be happening. There's also a lot of interesting news coming out of that, in terms of the activities that have gone on to reveal the information on American citizens that have been part of this, particularly General (Michael) Flynn. But I think there's a lot of areas that still need to be covered, there's a lot of information that still needs to be discussed."
Sean Spicer is eager to focus on who has been leaking information.
But he was quick to downplay the FBI investigation into Russian activities during the campaign and any links to the Trump campaign.
"Investigating it and having proof of it are two different things. You look at the acting Obama CIA director said that there is smoke but there's no fire.** Senator Tom Cotton (said), 'Not that I've seen and not that I'm aware of.' Senator Chris Coons, Democrat from Delaware, (said), 'I have no evidence of collusion.' I mean, there's a point at which you continue to search for something that everybody who's been briefed hasn't seen or found. I think it's fine to look into it, but, at the end of the day, they're going to come to the same conclusion that everybody else has had. So you can continue to look for something, but continuing to look for something that doesn't exist doesn't matter."
In Washington, Brookings Institute security and intelligence analyst Daniel Benjamin says the United States is heading into a situation possibly never seen before in US politics.
He says, if the President persists with his claims despite all evidence from top intelligence officials, it raises a potential crisis.
"There has never been anything quite like this in decades at least, since Watergate -- and, frankly, this is a lot bigger than Watergate -- and it doesn't appear that President Trump is going to change his tune on the wire-tapping. And so there's just this incredible cognitive dissonance, where we hear two different things going on. And, you know, it's a bit of a political crisis."
But amid the marathon grilling from the committee, there was some room for levity from James Comey when he was questioned about one of Donald Trump's outraged tweets.
(Questioner:) "The President accused Mr Obama, and, presumably, the FBI, of engaging in McCarthyism. Were you engaged in McCarthyism, Director Comey?"
(Comey:) "I try very hard not to engage in any isms of any kind, including McCarthyism."
