Flynn, in contrast, was a top adviser to the president in the White House before he was fired in mid-February, for lying to Vice President Mike Pence about his conversations with Kislyak. That made his tenure as national-security adviser historically brief. So far, the special counsel has released little information about the charges, but the two-page document indicates that Flynn’s conversations with Kislyak concerned presidential policy. According to the special counsel, Flynn spoke to Kislyak asking him to refrain from responding to new sanctions imposed in the waning days of the Obama administration, and that Flynn asked Kislyak to delay or defeat a UN Security Council vote; he then lied about those conversations with the FBI.

The fact that Flynn was operating on behalf of the incoming government represents the first concrete case of Trump’s presidential staff, rather than his campaign team, covering up contacts with Russia. Prosecutors said in court filings on Friday that Flynn called a “senior official of the Presidential Transition Team” on December 29, after being contacted by Kislyak, and was told that the transition did not want Russia to escalate the situation. Flynn then called Kislyak to request that Russia respond only in a reciprocal manner, which it subsequently did.

The filings also said that, on December 22, “a very senior member of the Presidential Transition Team” directed Flynn to contact officials from foreign governments about a pending UN Security Council resolution on the issue of Israel settlements, to find out where they stood and to persuade them to delay or defeat the resolution. Flynn made that request of Kislyak that same day, but Kislyak told him the following day that Russia would not oppose the resolution if it came to a vote. (It passed with 14 votes in favors, and only the U.S. abstaining.)

Third, the plea appears to corroborate reports that Flynn was working toward a deal in which he would plead guilty in exchange for cooperating with the government. That’s also bad news for the Trump administration, because it indicates that Flynn knows something of value to the special counsel’s investigation. Mueller’s choice of lieutenants has suggested he is seeking to flip key witnesses in order to learn essential information, but so far that had only yielded George Papadopoulos, a previously little-known campaign aide. Flynn is a far larger catch. In fact, one might expect the national-security adviser to be near the top of the food chain, since he reports directly to the president. If Flynn is small fry, how many bigger fish are there, and who?

Fourth, it’s notable that the charge against Flynn is lying to the FBI. That’s because it has been more or less known since February that he did so. On February 16, three days after Flynn’s forced resignation, The Washington Post reported both that Flynn had denied speaking with Kislyak about the sanctions in a conversation with FBI agents, and that intelligence intercepts indicated he was lying. The FBI interview took place on January 24; on January 26, then-Acting Attorney General Sally Yates spoke to White House Counsel Don McGahn, and in testimony in May she implied that she had informed McGahn that Flynn lied to FBI agents. The investigation into Flynn’s alleged lying to FBI agents long-predates Mueller’s appointment as special counsel in May.