This post has been updated.

When it comes to seminal moments in the Russia investigation that we will one day look back upon, Tuesday could be one.

The Post's Rosalind S. Helderman confirms that Michael Cohen's one-time business partner, Evgeny "Gene" Freidman (a.k.a. the "Taxi King"), has reached a plea deal with prosecutors and will cooperate with the government (the news was first reported by The New York Times):

Evgeny “Gene” Freidman, an immigrant from the former Soviet Union long known as the “taxi king” of New York, pleaded guilty to criminal tax fraud in Albany County Court. He is a former business partner of Cohen who managed taxis owned by the president’s lawyer for several years.
State prosecutors said Tuesday that Freidman, who operated 800 taxis between 2012 and 2015, failed to remit a 50-cent-per-ride tax owed to the state. Instead, he filed false tax returns designed to hide the theft, they said. During that period of time, he was operating taxis controlled by Cohen, according to people familiar with their relationship.

Both the timing and the circumstances are key. Freidman faced allegations that he failed to pay $5 million in taxes, including four counts of tax fraud and one of grand larceny. As part of the deal, he will serve no jail time. That suggests that he has been able to provide information of some value when it comes to Cohen, who is widely seen as a target for prosecutors to, in turn, flip against Trump.

“Do you understand the nature of the benefit your attorneys have accomplished on your behalf?” Judge Peter Lynch asked Freidman on Tuesday, according to the Times. That question should frighten both Cohen and President Trump's legal team.

There is no official indication that Freidman has agreed to inform specifically on Cohen, but it's not difficult to connect the dots. Freidman was first charged in June, but he has only now reached a plea deal as the noose has steadily tightened around Cohen's neck. And this isn't just an acquaintance; this was a business partner in an industry where Cohen's conduct has come under a microscope. If anybody knows about what Cohen has done wrong, Freidman may have been the most likely candidate — especially if Cohen did keep Trump in the dark about his Stormy Daniels payment and other matters.

Update: Freidman is reportedly downplaying the prospect of informing on Cohen.

Cohen's case isn't being handled by special counsel Robert S. Mueller III's team of investigators but instead by the U.S. Attorney's Office for the Southern District of New York, which received a referral from Mueller's team before raiding Cohen's office and home last month. But any plea deal could involve informing for the Mueller investigation.

Just as it has been clear that former Trump campaign chairman Paul Manafort was a target for flipping against Trump, Cohen's fate seems to revolve around whether he might be pressured into taking a deal, like Freidman was.

Cohen has said that won't happen, and Trump wagered last month that Cohen won't flip. But it looks increasingly like we're about to find out just how much pressure Cohen can withstand.