The White House snapped into damage-control mode as the testimony of former FBI director James Comey wrapped up on Thursday.

Now, this wasn't just any old Senate intelligence committee hearing: reporters lined winding corridors, people set up viewing parties and bars even opened early to take in the testimony of the guy unceremoniously fired by the president of the United States last month.

Comey testified that he believed Donald Trump tried to influence the FBI's investigation into Russian meddling in the U.S. election by requesting he drop the bureau's probe of former national security adviser Michael Flynn. And that the Trump administration lied when it initially claimed he was fired over "disarray" at the FBI.

"I know I was fired because of something about the way I was conducting the Russia investigation was in some way putting pressure on [Trump], in some way irritating him, and he decided to fire me because of that," Comey said.

'The president is not a liar'

So deputy press secretary Sarah Huckabee Sanders attempted to wrangle control of the message as Comey submitted himself to a second, closed-door session.

"The president is not a liar," she said.

And, as if on cue, other Republican faithful jumped in to complete the thought: He's just an idiot.

They didn't come right out and say that, of course, but the notion that the president of the United States might not totally understand what he's doing — or what it is he's supposed to be doing — has become an actual line of defence to explain away Trump's rather unpresidential behaviour.

Trump is 'new at this,' Republican House leader Paul Ryan said following Comey's testimony on Thursday. (J. Scott Applewhite/Associated Press)

House leader Paul Ryan, who was asked about Trump's alleged interference in the FBI's Russia investigation during his weekly press conference, explained that the president is simply "new at this" and might not totally understand that he's not supposed to stick his nose in an investigation that includes members of his administration.

"He's new to government, and so he probably wasn't steeped in the long-running protocols that establish the relationships between [the Department of Justice], FBI and White Houses," Ryan mused.

"He's just new to this," he reiterated.

Senator Marco Rubio — the guy Trump dubbed "Little Marco" during the Republican primary race — also fell into line, telling reporters after the hearing that Trump is a "non-politician" who perhaps "doesn't understand or, quite frankly, is not interested in convention."

Someone should have "advised the president about what's appropriate and what isn't when you're interacting with the FBI," he said.

In other words: OK, maybe Trump shouldn't have cleared the Oval Office that day back in February when he cornered Comey and allegedly suggested he "let go" of the Flynn investigation (a proposition Trump's lawyer claims was never actually floated), but please excuse the president's ill-considered request, he's just an idiot.

National security adviser H.R. McMaster said the president didn't know the source of the intelligence he leaked to the Russians. (Susan Walsh/Associated Press)

That's essentially what national security adviser H.R. McMaster said, in nicer words, when attempting to do some damage control after it was reported that Trump had leaked classified information to top Russian officials during a closed-door meeting back in May. "The president wasn't even aware of where this information came from," McMaster said about the top-secret intelligence, which was later confirmed to have come from the Israelis. "He wasn't briefed on the source or method of the information either."

In other words: He leaked this important information without understanding where it came from, or how it was retrieved, or why it is important. Cut him some slack, he's just an idiot.

To Ryan and Rubio's point, Trump is indeed a neophyte when it comes to being president. But so, too, were the dozens of men who occupied the Oval Office before him, yet most had the good sense to surround themselves with smart people — and actually listen to them. Trump, on the other hand, prefers to air his ideas to a Breitbart blowhard and his well-bred son-in-law — men he will listen to on occasion. But the voice he appears to listen to most often is the little one in his head that's probably reciting the chorus of We are the Champions right now while he pictures himself back onstage at one of his rallies.

Former FBI director explains why he believes he was fired and why he felt the need to document his conversations with U.S. President Donald Trump 1:34

To be fair, there are other, slightly more dignified defences being floated in response to Comey's testimony. They include the idea that the events as described simply never happened (Trump's lawyer), that Trump saying he "hoped" Comey would drop the investigation didn't constitute an order (Senator James Risch), that the actual scandal is Comey leaked a memo of his conversation with Trump to the press (Donald Trump Jr.), and that Hillary Clinton also did some bad stuff (Senator John McCain).

Nevertheless, it is remarkable that a go-to line being peddled by top Republicans is essentially that Trump didn't — and doesn't — know any better. Ignorance of the rules is a poor defence in most cases of misconduct, but apparently it's good enough to exonerate the guy in the White House.