The Defense Department’s inspector general is investigating whether former National Security Adviser Michael Flynn improperly took money from foreign governments after retiring from the Army, the latest sign that the disgraced retired general could be in serious legal trouble.

The investigation was made public Thursday as part of a set of documents released by Rep. Elijah Cummings, the top Democrat on the House Oversight Committee. In an April 1 letter to the Republican chair of the panel, Jason Chaffetz, the Pentagon inspector general said his office was looking into whether Flynn had “failed to obtain required approval” before accepting those payments.

Flynn’s new problems don’t stop there. Cummings also released a 2014 letter in which the Pentagon explicitly warned Flynn that there were restrictions on what he could accept — even as a retired officer — from a foreign government. Flynn, the Defense Department said, was barred from accepting money, gifts, or travel “unless congressional consent is first obtained.”

We now know that Flynn took the former without doing the latter. Flynn’s attorney said he informed the DOD that he was traveling to Russia to speak at an RT event, but wasn’t very specific on what he told them about payment. That could end up being a potentially serious problem.

More broadly, the key issue for Flynn, who was fired from his post as national security adviser after lying to Vice President Mike Pence about conversations with the Russian ambassador to the US, is money he received from the governments of Russia and Turkey and questions about whether he fully and honestly disclosed those payments.

Chaffetz, the Trump-friendly chair of House Oversight, released a withering letter on Thursday based on the documents his Democratic counterpart Cummings disclosed. Chaffetz flatly accused Flynn of violating laws barring retired military officers from taking foreign money without permission from the Pentagon.

“By all appearances, Lt. Gen. Flynn violated 37 USC 908 by accepting compensation from foreign governments without obtaining consent to do so,” Chaffetz wrote in the note, directed to the secretary of the Army.

Even if Flynn were found guilty, the punishment would be relatively light — a suspension of his pension payments from the military. But if Flynn lied on his paperwork about his foreign governments, or even continued to work on behalf of foreign interests while serving as national security adviser, the issue becomes much more serious.

“If he didn’t actually lie to anybody … it’s a slap on the wrist,” says Steve Vladeck, a law professor at the University of Texas who studies national security law. “But given all the noise that both DOD and the Oversight Committee are making, it sure seems like they think there’s more.”

The most serious possibilities, according to Vladeck, involve felonies — that is, jail time. If evidence of such charges emerges, then Attorney General Jeff Sessions will have a very difficult choice: prosecute a former Cabinet member from his own administration or explain why he’s letting a possible felon off the hook.

The four separate legal issues raised by Flynn’s conduct

In April 2014, the Obama administration pushed then-Lt. Gen. Flynn out of his job running the Defense Intelligence Agency (DIA). Like many retired generals and admirals, Flynn moved to the private sector, opening a small consulting firm. Unlike many retired generals and admirals, he agreed to work for two different foreign governments.

Flynn became a regular talking head on RT, Russia’s state-owned English-language news outlet. In December 2015, he was paid $45,000 for attending RT’s 10th anniversary gala. He sat next to Putin himself, and delivered a speech to the attendees about his view of the world. A recent Washington Post investigation found two more payments from Russian-affiliated companies totaling $22,500, also ostensibly for speeches.

In August 2016, Flynn’s consulting firm was hired by something called Inovo BV — a Dutch company that turned out to be a shell corporation for a wealthy member of the Turkish government. Flynn appears to have continued working for Turkey until November at the earliest, and was paid at least $530,000 by Ankara. During this time, he was also serving as a foreign policy adviser to the Trump campaign.

“Avoiding all of these questions is part of why prior administrations, of whatever ideological stripe, have been so obsessed with vetting”

US citizens, even retired military officers, can legally work on behalf of foreign powers and take money from them. That’s not, in and of itself, problematic.

But in order to do so legally, Flynn needed to be exceptionally honest to the US government about it — and cease his work as soon he reentered a position in the US government. And it’s not clear that he actually did all of the required steps.

According to Vladeck, this raises at least four separate legal questions — each of which, if borne out by the DOD or House Oversight Committee, could raise serious legal questions for Flynn. Here’s what they are, itemized:

Problem 1: lying about his status as a foreign agent

Under the Foreign Agent Registration Act (FARA), Flynn needed to publicly disclose any lobbying work he did with the Turkish government when he began doing it. At the time, Flynn’s FARA paperwork said he had worked for a Dutch company — not the Turkish government.

In March, Flynn filed paperwork correcting this error — admitting that Inovo was really paying him to work on behalf of Turkish interests. If that’s all he did, then he’s probably fine: The US government generally doesn’t arrest people for filing incorrect FARA paperwork after they correct it.

But if there was more undisclosed lobbying for foreign governments — more Turkey payments, or undisclosed activity for Russia — than he disclosed in March, then he’s potentially in serious legal trouble.

“The filing, if it’s incomplete, is actually a really big deal,” Vladeck says. “A filing that omits material information is, from DOJ’s perspective, an intentional violation of the statute [prohibiting lying].”

Problem 2: taking office while being a foreign agent

The other key question is when Flynn’s lobbying activities ended.

If he stopped lobbying for foreign governments in November 2016, as he said in his March FARA paperwork, then he’s probably fine. But if he actually worked on behalf of a foreign power after taking office on January 20, then he committed a felony.

“Accepting money from a foreign power while in office would be the easiest, most obvious, most simple case,” Vladeck says. “The harder question would be whether, based on prior agreements with foreign powers, he had any kind of continuing commitment to pursue particular policy initiatives or particular economic developments.”

This is the most serious charge facing Flynn; so far, there’s no evidence to support it. But it remains a possibility.

Problem 3: lying about his security clearance

In January 2016, Flynn filed paperwork — called an SF-86 — to renew his security clearance.

On the SF-86, you’re supposed to disclose any payments you get from foreign governments. But according to Chaffetz and Cummings, Flynn failed to mention the $45,000 he received from Russia to attend the RT dinner.

This, according to Vladeck, would constitute lying to federal investigators by making a “materially false” statement.

Problem 4: taking foreign money as a retired officer without permission

Retired military officers are not allowed, by law, to accept money from foreign governments without express permission from the DOD. The logic is that they could be called up at any time to active duty, and thus can’t be compromised.

Flynn, as far as we can tell, did not get such permission — that’s what Chaffetz’s note about “37 USC 908” is referring to, the statute that requires this permission.

The punishment here is civil, not criminal — just suspension of Flynn’s retirement pay, no jail time. This isn’t as serious an issue as the other three.

If Flynn committed a felony, the political ramifications could be enormous

Neither the House Oversight Committee nor the Pentagon, the two bodies we know are looking into Flynn’s contact with foreign powers, has the ability to prosecute him. If they find something damning, they refer the evidence to the Justice Department — which has final say on whether to pursue a criminal case against Flynn.

If that’s the case, then it falls to Attorney General Sessions to make the decision — unless he recuses himself or appoints a special prosecutor. This puts Sessions in a very tough place, politically.

If he prosecutes Flynn, he’d likely end up sending a top Trump ally to jail, embarrassing his administration severely. If he doesn’t, and lets Flynn off even though there’s good evidence that Flynn did something wrong, then it will look like Sessions is corrupt — covering for a political ally. The political backlash would be huge. (Back in late February, Senate Minority Leader Chuck Schumer called on Sessions to recuse himself from any investigation into Flynn.)

There’s one more wrinkle here. Flynn has offered to testify in FBI and congressional probes into Trump-Russia connections in exchange for immunity. So far, all investigating bodies have refused Flynn’s offer. But it’s possible that Flynn will end up telling investigators details about Trump and Russia that he’s held back so far if he feels like he’s facing the serious risk of prosecution (provided, of course, that he actually does have such information).

So Sessions letting him off the hook would be worse than just helping an ally: It could look like he was stymying the Russia investigation, from which he’d already recused himself due to his own lies about meetings with Russian Ambassador Sergey Kislyak.

What this shows, in short, is that the Trump administration’s willingness to appoint ethically dubious people to top-level posts is coming back to haunt them — creating at best a PR nightmare, and at worst a crisis.

“[This is] the broader context,” Vladeck says. “Avoiding all of these questions is part of why prior administrations, of whatever ideological stripe, have been so obsessed with vetting.”