(CNN) On Friday morning, former Trump campaign chairman Paul Manafort agreed to cooperate with special counsel Robert Mueller's probe into Russian influence and interference by the Russian government in the 2016 presidential election.

That plea deal, which comes on the heels of Manafort's conviction on eight felony counts of financial wrongdoing during a Virginia trial and on the verge of a second trial in Washington on similar charges, is a massive development -- and one that brings Mueller ever closer to President Donald Trump and his innermost circle.

Despite Trump's repeated assertions that Manafort was with his campaign for a very short time, the facts are these: Manafort ran the Trump campaign for an extremely critical period of time -- from April 2016, when he was brought in to fend off a possible delegate fight being launched by Texas Sen. Ted Cruz, until after the party's national convention in which Trump was formally nominated as the Republican presidential nominee.

During that period, Manafort was one of three senior Trump officials to participate in a June 2016 meeting with a handful of Russian officials -- a meeting that was premised on the promise of dirt on Hillary Clinton being provided by the Russians to the Trump campaign. According to Donald Trump Jr., the President's eldest son who helped organize the meeting and who was in attendance, there was no actual information on Clinton provided to him, Manafort and Trump's son-in-law Jared Kushner. It was merely a cover to get the Trump campaign brass in a room and lobby them about the Magnitsky Act

Manafort may well be the biggest of those dominoes to fall, due to the centrality of his role in the Trump campaign during a time in which we know the efforts by the Russians to influence the election were hot and heavy

The White House's attempt to downplay the importance of the Manafort cooperation deal purposely misses that point.

"This had absolutely nothing to do with the President or his victorious 2016 presidential campaign," said White House press secretary Sarah Sanders in the wake of the Manafort deal. "It is totally unrelated."

She's right that what Manafort pleaded guilty to on Friday -- one count of conspiracy against the US and one count of conspiracy to obstruct justice due to attempts to tamper with witnesses -- and what he was convicted of in Virginia last month have zero to do with the Trump campaign. All of the crimes Manafort has now copped to are related to work he did on behalf of the Ukrainian government long before he was named campaign chairman of the Trump bid -- and his admitted efforts to obstruct justice during his trial on those charges.

Manafort's attorney, Kevin Downing, said in a statement that his client has accepted responsibility and that he "wanted to make sure that his family was able to remain safe and live a good life."

But what Sanders' spin intentionally overlooks is the fact that what Manafort is pleading guilty to is of less importance than the fact that he is cooperating with Mueller. The financial crimes committed by Manafort in his dealings with the Ukrainian government are merely the lever by which Mueller and his special counsel team were able to exert pressure on Manafort to flip. Now that he has flipped, anything and everything is fair game. What Manafort knows about the Trump campaign, the Russia meeting at Trump Tower being only one piece of that, Mueller now knows. Or will know soon.

Even that prospect doesn't concern Trump and his legal team, according to lead lawyer Rudy Giuliani. "Once again an investigation has concluded with a plea having nothing to do with President Trump or the Trump campaign," Giuliani said in a statement. The reason: "the President did nothing." (Worth noting: That was the second version of the statement. The first also included a line insisting that "Paul Manafort will tell the truth." It was removed from the second statement.)

That confidence seems to crash directly into what appeared to be a public campaign led by Trump to keep Manafort from cutting a deal with Mueller. In late August, following Manafort's conviction in the Virginia trial, Trump tweeted these words of encouragement

"I feel very badly for Paul Manafort and his wonderful family. 'Justice' took a 12 year old tax case, among other things, applied tremendous pressure on him and, unlike Michael Cohen, he refused to 'break' - make up stories in order to get a "deal." Such respect for a brave man!"

Asked directly in a Fox News Channel interview whether he would consider a presidential pardon for Manafort, Trump refused to rule out the possibility -- saying he had "great respect" for his former campaign chairman. "One of the reasons I respect Paul Manafort so much is he went through that trial," Trump said. "You know, they make up stories. People make up stories."

To be clear: Solely because Manafort has agreed to become a cooperating witness doesn't mean that Trump -- or even Trump Jr. or Kushner -- is guilty of anything. It's possible that Manafort will simply corroborate the details that others within the Trump inner circle have already offered up about who knew what and when about Russia's efforts to elect the billionaire businessman.

That said, it's hard to imagine that Mueller would agree to a plea deal with Manafort -- thereby lessening his charges from what could have been eight decades down to just 10 years maximum -- if he didn't think the former campaign chairman had worthwhile information. Manafort had already been convicted in Virginia and, by all accounts, the case against him in DC was even stronger. So why cut a deal with a guy who a) has already been convicted and b) could face even more jail time with a subsequent conviction?

I'm no lawyer -- sorry Mom! -- but common sense dictates that Mueller would only proffer such a deal if he knew that Manafort could help him shed light on events involving people higher up the food chain. And given that Manafort was the campaign manager for Trump, there just aren't a lot of people above him. And those who are either related to the President of the United States or are the President of the United States.