"Michael Cohen, President Donald Trump's former personal attorney, claims that then-candidate Trump knew in advance about the June 2016 meeting in Trump Tower in which Russians were expected to offer his campaign dirt on Hillary Clinton, sources with knowledge tell CNN. Cohen is willing to make that assertion to special counsel Robert Mueller, the sources said."

Holy crap.

Let's take a quick step back for some context. The June 2016 meeting between a group of Russians and the top brass of the Trump campaign, including the candidate's eldest son and son-in-law, has long been at the center of questions -- from special counsel Robert Mueller and others -- about whether there was any sort of collusion between a foreign country and the Trump campaign in 2016. When news of the meeting first broke, Donald Trump Jr. insisted it was a brief and unimportant gathering focused on an obscure adoption law that the Russians wanted changed.

But as the story came into closer focus, it became clear that the genesis of the meeting was a promise on behalf of the Russians, by a go-between named Rob Goldstone, that they had dirt on Hillary Clinton that they wanted to pass along to the Trump brain trust. "Seems we have some time and if it's what you say I love it especially later in the summer," Trump Jr. wrote in an email to Goldstone about the promised dirt.

We also later learned that Trump himself had been involved in the crafting of his son's initial statement to the media about the meeting, a revelation that contradicted past claims that he was uninvolved. In June, The New York Times revealed that not only had the President known about the statement, but that he had dictated himself.

Which brings us to this allegation regarding when Trump knew -- and if he knew -- about the Trump Tower meeting before it happened.

Trump himself has been absolutely conclusive that he did not have any foreknowledge of the meeting. "No, I didn't know anything about the meeting," he told The New York Times during an interview in July 2017 . "It must have been a very important -- must have been a very unimportant meeting. ... No, nobody told me. I didn't know noth-- It's a very unimportant -- sounded like a very unimportant meeting. Because I never even heard about it."

He doubled down on that position Friday morning: "I did NOT know of the meeting with my son, Don jr. Sounds to me like someone is trying to make up stories in order to get himself out of an unrelated jam (Taxi cabs maybe?). He even retained Bill and Crooked Hillary's lawyer. Gee, I wonder if they helped him make the choice!"

Trump Jr. said much the same during a behind-closed-doors meeting of the Senate Judiciary Committee. "No, I wouldn't have wasted his time with it," Trump Jr. said when asked whether his father knew about the June 2016 Trump Tower meeting in advance. (The testimony was released publicly.)

So. Someone is not telling the truth here. If Cohen can make good on his allegation that Trump knew about the meeting prior to it happening -- and perhaps provide corroborating witnesses to that effect -- it would not only prove the denials by the President and his son wrong, but it would be the biggest step to date in proving (or at least suggesting) real collusion between the Trump team and the Russians. If Cohen is bluffing or can't deliver what he claims, then this is the political equivalent of Al Capone's vault -- much ado about nothing.

The problem here is that neither Trump nor Cohen have a stellar record when it comes to facts. Trump said more than 3,000 untrue or misleading things in just his first 466 days in office, according to The Washington Post's Fact-Checker blog. And Cohen endeared himself to Trump over the years by a demonstrated willingness to say and do whatever it took to solve problems for his boss. (Remember that Cohen insisted Trump knew nothing of the $130,000 payment to porn star Stormy Daniels just 11 days before the 2016 election, even though it later came out that Trump had reimbursed him for that payment.)

In the immediate aftermath of the Cohen bombshell -- or, better put, the potential Cohen bombshell -- Trump lawyer Rudy Giuliani sat down with CNN's Chris Cuomo to offer a rebuttal. And it consisted entirely of questioning Cohen's credibility.

"I expected something like this from Cohen," Giuliani said. "He's been lying all week. He's been lying for years."

Later, Giuliani added: "I don't see how he has any credibility."

The potential problem with that argument is that for those "years" that Giuliani is referring to, Cohen was one of Trump's closest advisers. In fact, up until Cohen made clear in an interview earlier this month with ABC's George Stephanopoulos that his loyalty to Trump was fading, the President was defending Cohen on Twitter and insisting that he would never "flip." It's only in the last few days -- first with the release of an audio tape of Trump and Cohen chatting about former Playboy model Karen McDougal and now this allegation -- that the Trump team has turned on Cohen so aggressively.

Knowing that Cohen's credibility is everything at this point, his legal team -- led by Lanny Davis -- has been on a bit of a public relations push of late, arguing that Trump's former fixer is a changed man. "This man has turned a corner in his life, has hit a reset button, and he's now dedicated to telling the truth," Davis told Cuomo earlier this week

There are now two major questions that matter going forward on this story:

Will Cohen actually tell Mueller what he knows about the alleged foreknowledge Trump had of the June 2016 meeting? If he does, will the case Cohen can make be enough to convince Mueller? Or does Mueller find the Trump denials more credible?

In short: Where have you gone, Robert Mueller? Our nation turns its lonely eyes to you.