The latest ominous chapter in the Russiagate scandal started to play out yesterday when it was reported that Michael Flynn, Trump’s ousted National Security Advisor, had offered to testify before Congress in exchange for a grant of immunity.

Flynn’s attorneys presented this offer with the teaser that Flynn “certainly has a story to tell.”

Indeed he does.

A month and a half ago, shortly after Flynn was fired as President Trump’s National Security Advisor, I published an article predicting that the Flynn affair had the potential to bring down Trump’s presidency (“The Flynn Affair Could Bring Down Trump’s Presidency”).

The gist of it was that Flynn’s firing could be the beginning of the end for Trump, and that the story would only get bigger in the weeks and months ahead.

Trump’s silence about whether Flynn had discussed sanctions with Russia in the midst of the election, while everybody else around Trump was loudly denying it, seemed strangely out of character.

That is, unless Trump knew he had something to hide.

Trump may not only have known about Flynn’s dangling the easing of sanctions in front of the Russians, he may have ordered it. Either way, complicity in highly improper, and possibly illegal communications with Russian agents could lead to Trump’s impeachment.

Since Trump and Flynn could be the only two people with direct knowledge of what took place between the two of them and the Russians, a lot depended on Flynn’s reaction to his ouster. It was certainly possible that he would play the good soldier and keep his mouth shut, including possibly asserting the 5th Amendment if required to testify.

But if Flynn decided to talk, he could bury Trump.

Well, the story just got a lot bigger.

Now it looks like Flynn is prepared to bury Trump, not to praise him. All it may take is a grant of immunity.

It is too soon to know whether the House or Senate Committees, or the FBI, will accept Flynn’s offer of testimony in exchange for immunity.

First, they have to decide whether they want to accept the offer.

A decision to accept or reject Flynn’s offer will depend on several factors. Obviously, the committees will have to be convinced that the story that Flynn has to tell is worth granting him immunity. That will likely depend initially on obtaining a preview of Flynn’s likely testimony, known as a legal “proffer,” through his attorneys.

If the proffer is sufficiently tantalizing, the committees will need to determine whether the evidence Flynn would supply through his testimony is available from some other source. That source would not necessarily be another witness. It could be documents or information received through electronic surveillance.

Next, the committees will have to consider whether Flynn was the kingpin of whatever misconduct took place, or just a mid-level miscreant. In other words, they need to decide whether Flynn can help them land a bigger fish.

Like Trump, for instance.

Once they decide that the deal is worth making, they will have to discuss their decision with law enforcement authorities and the Department of Justice prior to executing a grant of immunity. Neither the FBI nor the Department of Justice has the authority to prohibit a grant of immunity, but they could effectively kill it anyway.

A grant of immunity will not necessarily shield Flynn from prosecution, but the DOJ and law enforcement will give any proposed deal careful scrutiny. Depending on the specifics of the deal, Flynn could be shielded from having his testimony used in a prosecution, but not from being prosecuted on the basis of evidence obtained elsewhere. Nevertheless, granting immunity could present a serious roadblock to prosecution because of the difficulty in convincing a court that the evidence presented had been obtained entirely independently from Flynn’s immunized testimony.

If law enforcement or the DOJ put up enough of a fuss that a grant of immunity to Flynn will seriously interfere with an ongoing criminal investigation or prosecution, it is unlikely that the committees will be able to muster enough support to make the deal.

Granting immunity will require approval by 2/3 of the committee members. That means that neither the Democrats nor the Republicans can do it alone. Achieving that level of consensus would be a tall order under any circumstances, but strong resistance from the FBI or DOJ would probably make it impossible.

So there’s a bit of a journey from here to there.

But if they get there, Flynn will presumably tell all he knows. He will have every incentive to tell the truth because obtaining immunity will not shield him from prosecution for perjury. And he will not be able to assert a privilege under the 5th Amendment because his immunity will have already assured that his testimony can’t be used against him.

None of this will happen overnight.

But it sure feels like the Russiagate impeachment train has just left the station.

Philip Rotner is an attorney and an engaged citizen who has spent over 40 years practicing law. His views are his own and do not reflect the views of any organization with which he has been associated. Follow Philip on Twitter at @PhilipRotner.