Ed. note: This article was published before special counsel Robert Mueller charged former National Security Advisor Michael Flynn with one count of making a false statement to the FBI about his contacts with Russia.

Special Counsel Robert Mueller’s Russia investigation may be heading toward a major turn, if recent hints that former National Security Advisor Mike Flynn is cooperating with the probe pan out.

Flynn — who departed the White House after revelations that he obscured his contacts with Russian officials — became a top Trump ally when the real estate mogul’s campaign still seemed like a long shot. The retired general remained a crucial figure through the transition and early days of the administration.

There are now signs that the special counsel may be in the process of flipping Flynn, with news that his legal team has stopped collaborating with President Trump’s, as well as reports that Flynn’s lawyer met with Mueller’s team Monday. Such moves aren’t guarantees that Mueller has turned Flynn — let alone turned Flynn against President Trump or his inner circle. Yet Flynn would be an extremely valuable witness to Mueller, perhaps more valuable than the other campaign figures who have been swept up in Mueller’s investigation.

There are a handful of known examples placing Flynn in the middle of Trump world interactions with Russian figures — interactions the White House has sought to downplay. Then there is Trump’s continued loyalty to Flynn, who was fired in February — a loyalty that raises a flag for former prosecutors.

“Trump’s not the type of guy who goes out of the way for anybody. Why would he be so concerned about Flynn and saying such nice things about Flynn?” Nick Akerman, an assistant Watergate prosecutor, told TPM.

“So what is it that Flynn knows and who is it that Flynn knows it about? Is it Trump? Is it Kushner? Is it Don Jr.? Is it all of the above?” Akerman said.

It may be many months before we know exactly what Flynn has to offer Mueller — or if any offer is even being made. But there are plenty of reasons to believe his cooperation could be problematic for Trump and his inner circle.

Kushner’s ‘Backchannel’ Idea

Flynn was present at a Dec. 1 Trump Tower meeting where Kushner reportedly proposed to Russian Ambassador Sergey Kislyak that they set up a backchannel for transition team communications with Moscow.

Since the meeting and the backchannel idea were initially reported, Kushner has pushed back on claims of impropriety. In a statement to congressional investigators, Kushner said that Kislyak had bought up having his “generals” brief Flynn on working with the U.S. in Syria.

“I asked if they had an existing communications channel at his embassy we could use where they would be comfortable transmitting the information they wanted to relay to General Flynn,” Kushner said. “The Ambassador said that would not be possible and so we all agreed that we would receive this information after the Inauguration.”

The meeting, which the White House only acknowledged in March after media reports about it, is one of a series of examples of Trump associates not disclosing their contacts with Russians during and after the campaign.

Pre-Inauguration Sanctions Talk With Russia

What ultimately led to Flynn’s White House ouster was previously undisclosed contacts he had with Russian officials before the inauguration, including one conversation where he reportedly discussed sanctions the Obama administration was imposing on Russia in late December.

The White House’s story about Flynn’s sanctions-related conversation with Kislyak changed drastically as the details about it were reported. Most notable perhaps was the stern denial by Vice President Mike Pence in January that sanctions were discussed.

A GOP Operative’s Hunt For Clinton’s Emails

The veteran GOP operative who launched a freelance campaign to obtain emails stolen from Hillary Clinton’s personal server during the 2016 race boasted of support from two key backers: Flynn and his son, Michael Flynn Jr.

In recruiting emails to computer security experts, the operative, Peter W. Smith, said Flynn’s consulting firm was assisting his effort to obtain the emails, which Smith told the Wall Street Journal he understood were likely hacked by Russian operatives.

A British security analyst contacted by Smith said their communications made it “immediately apparent that Smith was both well connected within the top echelons of the campaign and he seemed to know both Lt. Gen. Flynn and his son well.”

Smith, who died in May, name-dropped other Trump campaign officials he claimed were working with him, including former chief White House strategist Steve Bannon and White House counselor Kellyanne Conway, in a recruiting document. Both have denied any involvement.

White House Knowledge Of Flynn’s Other Foreign Dealings

Senior transition and White House officials were warned on multiple occasions about Flynn’s work for foreign governments.

Vice President Mike Pence was informed about Flynn’s lobbying on behalf of Turkey in a November 2016 letter from Rep. Elijah Cummings (D-MD); Flynn reportedly notified transition team chief lawyer-turned-White House counsel Don McGahn that he was under federal investigation for that work weeks before inauguration; and former Acting Attorney General Sally Yates told McGahn in late January that Flynn was “compromised with respect to the Russians.”

Yet Flynn stayed in office for 18 days after Yates’ urgent warning, and the White House has insisted he was fired only for lying to Pence about his contacts with Russians.

So what did White House officials know about Flynn’s foreign dealings and when exactly did they learn it?

Trump Runs Interference For Flynn With Comey

At an infamous Feb. 14 meeting, the day after Flynn was fired, Trump reportedly said to then-FBI Director James Comey: “I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy.”

Trump has denied making this request, which Comey testified before Congress that he took as “a direction” that left him “stunned.” The former FBI director has turned over to Mueller contemporaneous memos he kept of his one-on-one conversations with Trump.

Comey also said the President never inquired about any other investigation.

This spring, Flynn reportedly assured associates he would remain loyal to the President and made the remarkable admission that Trump told him to “stay strong” during the investigation. Former prosecutors warn that such ongoing conversations could be portrayed as witness tampering.

Possible Policy Quid Pro Quo

Flynn accepted hefty sums to smear a Muslim cleric loathed by Turkey’s government, and reportedly offered to spirit him out of the country for even more money. But did he take additional steps during the transition or administration on Turkey’s behalf?

Flynn brought Bijan Kian, his Flynn Intel Group partner who spearheaded the anti-cleric lobbying contract, onto the transition team to advise on national security issues. Kian is now reportedly a subject of Mueller’s investigation.

As McClatchy reported, just days before inauguration, Flynn put a hold on a military operation to retake the Islamic State stronghold of Raqqa that Turkey opposed because it relied on assistance from Syrian Kurdish forces.

The Trump administration ultimately approved the plan weeks after Flynn was fired.

Akerman, the former Watergate prosecutor, said that Flynn’s decision held off the invasion “for a long period of time, putting people’s lives in jeopardy.”

“It really is pretty outrageous, so what did Trump know about that? And about [Flynn’s] involvement with Turkey?” Akerman asked.

The Trump Campaign’s Other Russia Shenanigans

Where Flynn fits in with the other areas of reported contacts between Trump campaign associates and Kremlin-linked figures is still an open question.

Flynn is not among the campaign officials identified in court documents about campaign foreign policy adviser George Papadopoulos’ own Russia-related contacts. Another foreign policy adviser Carter Page, in testimony to the House Intel Committee, denied communications with Flynn, though he did tell other campaign officials about a 2016 trip to Moscow. And The Atlantic’s report on private messages between Donald Trump Jr. and Wikileaks’ Twitter account did not include Flynn among the campaign officials Trump Jr. informed about his Wikileaks contacts.

If Flynn has more to add about those shenanigans, it could be useful to Mueller as well.