Former national security adviser Michael Flynn arrives for his plea hearing at the E. Barrett Prettyman Courthouse in Washington on Friday. (Chip Somodevilla/Getty Images)

Randall D. Eliason teaches white-collar criminal law at George Washington University Law School.

Former national security adviser Michael Flynn pleaded guilty Friday in federal district court to one count of lying to the FBI in connection with the Russia probe. Flynn admitted that he lied during an interview on Jan. 24 about contacts he had with the Russian ambassador to the United States in December.

A guilty plea by someone who was such a key part of President Trump’s inner circle is undoubtedly a significant development in the investigation by special counsel Robert S. Mueller III. At the same time, it’s important not to get too far out ahead of this story. We can glean enough information from the plea to know that this may be an ominous sign for the White House, but there’s still much that we don’t know about the plea’s implications.

Flynn pleaded guilty to a single count of false statements, a felony that carries a sentence of up to five years. This is the same charge that George Papadopoulos pleaded guilty to in October. Papadopoulos and Flynn admitted to similar crimes: lying to the FBI during the week after Trump’s inauguration about contacts they had with Russian individuals while working for the campaign or the presidential transition. In both cases, although Mueller’s team is bringing the charges, the lies to the FBI took place several months before Mueller was appointed.

As felony charges go, false statements is a relatively minor one. Flynn’s plea agreement stipulates that it likely will result in no jail time at all. The accusations swirling around Flynn for the past few months included multiple possible charges of failing to register as a foreign agent, several false written and verbal statements, money laundering and even potential involvement in a kidnapping plot involving a Turkish cleric. In light of all those allegations, being allowed to plead to this single charge seems like a sweet deal.

The court filings in connection with the plea reveal the likely reason Flynn was able to get that deal: He has agreed to cooperate in the special counsel’s investigation. In exchange, prosecutors have agreed not to pursue additional charges related to his lies to the FBI and not to charge Flynn for false statements he made when he belatedly registered last March as a foreign agent of Turkey. They may even have agreed to show leniency toward Flynn’s son, who reportedly faced legal troubles of his own. But the plea agreement does not appear to prohibit the special counsel from later pursing charges in completely different areas, including other false statements or obstruction, money laundering or the alleged kidnapping plot. That could mean prosecutors have concluded those charges are without merit, or could indicate there are still some areas of potential leverage over Flynn that prosecutors have held back.

Flynn’s cooperation will likely include grand jury testimony and, if necessary, trial testimony, as well as providing all documents and information that he has related to the ongoing investigation and potential criminal acts by others. Those others typically would be “bigger fish” higher up the food chain of potential targets.

Like Papadopoulos, Flynn pleaded guilty to lying about matters that directly relate to Russian contacts with Trump officials. Unlike with the indictment of Paul Manafort, therefore, the White House will not be able to claim that these charges are completely unrelated to the president or his campaign. This is particularly true considering the plea documents indicate that Flynn was communicating with more senior members of Trump’s transition team about his contacts with the ambassador. And unlike Papadopoulos, Trump officials will not be able to dismiss Flynn as some low-level, insignificant volunteer. On the other hand, the Russian contacts that Flynn lied about took place in December and so could not have directly related to any Russian efforts to influence the election. By contrast, Papadopoulos pleaded guilty to lying about contacts with Russians that took place during the campaign and before the election.

But regardless of whether meetings took place before or after the election, the obvious question on prosecutors’ minds will be: Why lie? Was it merely to cover up premature, improper diplomatic dealings with Russia on behalf of the incoming administration? Or was there a broader purpose: to conceal a more extensive array of ties and contacts between the Trump campaign and administration and the Russians?

Much of this remains speculation. Everything hinges on exactly what information Flynn can provide, and we are not likely to know that any time soon. Mueller’s shop has been pretty tight-lipped, and these investigations can take some time. It’s certainly possible, as the White House is claiming, that Flynn simply is pleading guilty to essentially the same lies that led to his resignation and that the investigation will not reach any further into the administration. And it’s important to keep in mind that neither Flynn nor Papadopoulos actually pleaded guilty to anything approaching a conspiracy with Russians to influence the election.

But given what we know about the nature of these types of investigations, Friday’s news has to worry the White House. As with the charges unveiled against Manafort and Papadopoulos several weeks ago, Flynn’s plea has all the hallmarks of the latest step in a classic white-collar investigation that is methodically building cases against people on the lower rungs, flipping them, and moving up the ladder. And once you get as far up the ladder as Flynn, there aren’t that many rungs remaining.