Flynn flipping is a major break for Mueller and bad news for the next big target

Michael Flynn was a key player in Donald Trump's orbit, including his election campaign, his transition teamand, at least for a few days, in his White House.

All the more reason why the retired general will prove very valuable to the U.S. special counsel investigating possible ties between Trump's presidential campaign andRussian election-meddlers.

Flynn, Trump's short-lived national security adviser, is the first senior official to cave to Robert Mueller's probe. He pleaded guilty on Friday to lying to the FBI about his talks with the Russian ambassador last December.

• Trump stresses'no collusion' after Flynn's guilty plea

It was part of a plea deal with Mueller's team as they pressure figures around president Trump to co-operate with their investigation.

With Flynn helping them, that pressure will be applied in one direction.

"Upwards," said Barak Cohen, a former federal prosecutor.

"They're going to take that information Flynn has provided, and they'll keep going as high up the food chain as it gets," he said. "They won't stop until they're satisfied they've reached as far as they reasonably can."

Flynn's co-operation not only suggests he has information Mueller's team finds crucial to the case, but that a pre-agreement sit-down called a "proffer of information" gave prosecutors enough confidence in Flynn's answers to warrant offering him a deal.

Flynn's guilty plea for lying to the FBI a felony that carries a maximum five-year sentence is an "inflection point" in the case, Cohen said.

With Flynn now feeding information to prosecutors, "they're reaching a point where they're going to start involving more significant figures," including possible "dotted line" connections between Flynn and the president.

'Co-operate up'

Dan Richman, the Columbia University law professor and friend of former FBI director James Comey who leaked Comey's memo detailing conversations with Trump, said in an interview that "no reputable prosecutor" would accept a co-operatorthey haven't already carefully vetted through debriefings.

So Flynn was likely sharing knowledge with Mueller's team before Friday's plea agreement.

"How long that would take, whether a number of days or weeks, is anyone's guess," Richman said.

Bob Mueller is pursuing the evidence, he's pulling threads to see how it unravels, and General Flynn is the biggest thread to date- Jeff Cramer, former U.S. federal prosecutor

Prosecutors, he said, generally agree to deals with informants who will "co-operate up," rather than to implicate subordinates. Depending on what evidence Flynn is illuminating, he said, "anyone who has had dealings with Flynn should now be reconsidering their position."

What Flynn can tell prosecutors includes details about campaign, transition and administration meetings; information about the nature of his talks with Russians and who in Trump's circledirected those contacts; and insight into the power structure inside a White House lacking a clear hierarchy of influence below the president.

Mueller's targets might include senior campaign advisers, transition team members and current White House top brass. And that could meanmembers of Trump'sfamily.

U.S. media outlets reported that the Trump confidant who allegedly instructed Flynn to contact Russian Ambassador SergeyKislyak last year was the president's son-in-law, Jared Kushner. (The charging document only refers to this unnamed official as a "very senior" transition member.)

If confirmed,Kushner'sinvolvement would be significant because among the false statements Flynn admits to giving to FBI agents was his denial that he ever askedKislyak"to delay the vote on or defeat a pending United Nations Security Council resolution"on the building of Israeli settlements.

Last week, Mueller's team reportedly interviewed Kushner about a meeting with the Russian ambassador. In the context of the Flynn revelations, University of St. Thomas legal scholar Mark Osler, a former federal prosecutor, said Kushner might have been asked a set of "control questions" to see if he would validate what prosecutors already knew via the Flynn proffer sessions.

"You're going to use different witnesses to corroborate one another, or to figure out who's lying to you," Osler said.

U.S. prosecutors already indicted former Trump campaign manager Paul Manafort and his second in command on the campaign, Rick Gates, for alleged financial crimes. A third person, GeorgePapadopoulos, a former campaign policy adviser whom the White House brushed off as a "low-level volunteer," also pleaded guilty to lying to FBI investigators.

The president dismissed those figures asmarginal players, with a former campaign adviser callingPapadopoulosa "coffee boy."

Trump'slawyer, Ty Cobb, tried the same spin Friday when he issued a statement that downplayed Flynn as a "former Obama administration official" who served for 25 days. There was no mention that Flynn led campaign rally chants and occupied one of the most sensitive roles in Trump's inner circle as national security adviser.

"It's hard for any objective individual to say he's not really close to the president," said Jeff Cramer, a former federal prosecutor in Chicago. "Bob Mueller is pursuing the evidence, he's pulling threads to see how it unravels, and General Flynn is the biggest thread to date."

Cramer said Flynn's chargeof providing false statements is narrow, considering what's known about his payments for lobbying work on behalf of the Turkish government, and allegations he and his son plotted to kidnap a Turkish cleric living in the States, among other things.

The one charge waslikely simply a wayto get him into court, Cramer said.

"View this in the prism of just locking him into a plea so he can co-operate, and it makes sense," he said. "They could have charged him with jaywalking."

Opting not to provide an extensive list of Flynn's possible transgressions also allows Mueller to conceal how much he knows, so as not to tip off others who might be implicated later. And as legal scholar Mark Osler points out, Mueller can dangle the more serious charges above Flynn's head to make sure he continues to co-operate.

While a sitting president can't be prosecuted, Trump's family members could be vulnerable to charges if collusion or obstruction of justice is found, he said.

As for the risk to the president, Osler offered one way the president's position could be jeopardizedby an obstruction of justice charge even if he can't be tried.

"That," he said, "would be impeachment."

Major players in the Russia Investigation so far: