Washington (CNN) At a joint news conference with Colombian President Juan Manual Santos Thursday, President Donald Trump was asked a very simple question: Had he urged then-FBI Director James Comey to slow or stop an FBI investigation into deposed national security adviser Michael Flynn?

It was over in a flash. But in those four words, Trump staked the viability of his presidency.

Why? Because he directly contradicted the reporting around a memo that Comey had written in the wake of a February 14 meeting in which Trump told him to see if he could find a way to end the Flynn investigation, The New York Times first reported and CNN confirmed

Both of those things can't be true.

Comey, who was fired by Trump 10 days ago, is expected at some point in the not-too-distant future to come to Congress and testify about his meetings with Trump. And the relevant congressional committees have already requested the February 14 memo as well as any other memos -- and CNN has reported there are more of them -- that Comey wrote about his interactions with Trump.

Between his testimony and the memo(s), Comey's side of the story is going to get out there. And, presuming that what we know of the February 14 memo is true, then Trump's former FBI director will be on record directly disagreeing with the President's version of events.

By issuing such a blanket denial, Trump leaves himself very little wiggle room. In order for Trump to emerge unscathed, there can be no evidence that emerges that props up Comey's side of the story. Anything that shows Trump was not being entirely truthful with his "no, no, next question" response calls into question his credibility on a whole range of issues and could well lead to open revolt from within his own party.

Trump's situation here is not dissimilar to that of New Jersey Gov. Chris Christie, one of the early Trump converts. After the news broke that two of Christie's top gubernatorial aides had been involved in a political payback ploy that involved closing lanes of traffic in Fort Lee, New Jersey, Christie went on record to say he was totally unaware of any of this plotting.

Had anything come out that proved Christie even slightly wrong in that total denial, it would have been curtains for his political career. It never did -- and Christie survived. (As it was, the Bridgegate scandal badly hamstrung Christie and he never was a real factor in the 2016 race.)

In short: The story of the February 14 meeting is currently a "he said, he said" one. If it never progresses beyond that, Trump will almost certainly survive, politically speaking. There will be plenty of grumbles from Republicans -- many of whom are on the record praising Comey as a trustworthy guy and able public servant -- but short of evidence that tilts the scales in Comey's favor, it will be very hard to abandon Trump.

If, on the other hand, tapes -- like the sort Trump floated he might have of his conversations with Comey -- or any other sort of documented evidence emerges that poke holes in Trump's four-word denial, he and his presidency will be in deep trouble.

Donald Trump is a gambler by nature. Repeatedly during his presidential campaign, and now in the White House, he has rolled the dice and reacted once they settled. But, whether he realized it at the time or not, Trump placed the biggest bet of his political career on Thursday.

Now he waits to see if it pays off -- or if he goes bust.