Did Sally Yates, then the acting attorney general, warn White House Counsel Don McGahn on Jan. 26 that National Security Adviser Mike Flynn had misled the FBI? Did McGahn relay that warning to President Trump? And did Trump decide it wasn’t legally problematic or serious enough to oust Flynn? That sequence needs to be investigated now that the Washington Post has disclosed what Flynn apparently told the FBI.

Here’s the basic story. On Dec. 29, Flynn had a phone call with Russian Ambassador Sergey Kislyak. According to U.S. intercepts of the call, Flynn told Kislyak that the incoming Trump administration would review sanctions that had just been imposed on Russia by the Obama administration for interfering in the election that installed Trump. Two weeks after the call, around Jan. 13 or 14, Flynn told the White House that he and Kislyak hadn’t talked about the sanctions. Based on this misinformation, Vice President Mike Pence and White House press secretary Sean Spicer publicly denied that the sanctions had been discussed.

Intelligence and FBI officials had seen a secret report on the intercepts of the call. They knew Flynn had misled Pence and Spicer. They wanted to warn the White House. They had three concerns. One was that Flynn’s offer to review the sanctions might have violated the Logan Act, an old law that prohibits private citizens (which Flynn was at the time) from meddling in diplomacy. A second concern was that Russia could blackmail Flynn, since it knew the story he had told Pence was false. A third concern was that Pence needed to know he was being deceived.

But that wasn’t enough for FBI Director James Comey. According to a Washington Post report from Tuesday, Comey told Yates, CIA Director John Brennan, and Director of National Intelligence James Clapper that before they alerted the White House, they needed something more:

On Obama’s last full day in office, Jan. 19, Clapper and Brennan made the case to Comey for informing the Trump team about Flynn. The FBI director pushed back primarily on the grounds that notifying the new administration could complicate the agency’s investigation. The bureau, Comey also insisted, shouldn’t be “the truth police,” according to an official familiar with his thinking at the time. “In other words, if there’s not a violation of law here, it’s not our job to go and tell the vice president that he’s been lied to.”

In the days following Trump’s inauguration, FBI agents interviewed Flynn about his calls with Kislyak. That removed the basis for Comey’s earlier objection to notifying the White House, current and former officials said. It is unclear whether Flynn gave the agents an accurate account of his calls with Kislyak. If not, officials said he could find himself in serious legal jeopardy.

The implication of these two paragraphs seems clear: The FBI interviewed Flynn on Jan. 24 to meet Comey’s standard. The interview produced the requisite violation of the law. The Post’s Thursday update indicates that the violation was Flynn’s false denial. The Post notes that Flynn “followed his denial to the FBI by saying he couldn’t recall all of the conversation,” and a CNN report posted Friday morning says that after the agents “challenged” Flynn, he said he didn’t remember. The FBI decided the interview wasn’t enough of a basis to prosecute Flynn. But according to both CNN and the Post, it was enough to satisfy Comey that Yates could warn the White House.

So she did. According to a Tuesday briefing by Spicer, on Jan. 26 Yates “informed the White House Counsel that they wanted to give a ‘heads up’ to us” about Flynn’s deception. The Post reported that Yates’ warning to McGahn included something Spicer didn’t mention in his Tuesday briefing: the danger that Flynn was “vulnerable to Russian blackmail.”

It’s not clear what Yates told McGahn, if anything, about the FBI interview. Maybe, to protect the Flynn investigation, she didn’t mention it. But it would be odd to delay warning the White House for lack of a crime, then send agents to interview Flynn to produce that crime, and then not mention or at least allude to that crime in the warning. Spicer says that at the time, Yates “could not confirm there was an investigation.” That remark by Spicer suggests that Yates withheld explicit confirmation but that something in her words made McGahn suspect Flynn was in legal trouble with the FBI and that the bureau had begun taking its usual steps, which would include an interview.

If McGahn knew or suspected that the FBI had interviewed Flynn, the next question is what McGahn told Trump. According to Spicer’s account, McGahn briefed Trump and his senior advisers “immediately” (not including Pence, apparently) and, at Trump’s direction, “undertook an extensive review” that included studying “materials” and interrogating Flynn “on several occasions based on information that was provided.” Spicer acknowledged that as part of this process, there was “communication between the Department of Justice and the White House Counsel’s Office.” But he refused to say what that entailed. The bottom line, said Spicer, was that Trump concluded “Gen. Flynn did not do anything wrong, and the White House Counsel’s review corroborated that.”

At his press conference Thursday, Trump said nothing he had heard from McGahn made him think Flynn was guilty of more than misleading Pence. Trump recalled that the “information” had come from Yates, the acting attorney general, and that “I was a little surprised, because I said, ‘Doesn’t sound like he did anything wrong.’ ” Trump was asked whether the White House had looked at transcripts of the intercepts or other evidence, but he didn’t answer. When a reporter asked why Trump had kept Pence in the dark about McGahn’s information for nearly two weeks, Trump replied: “Because when I looked at the information, I said, ‘I don’t think he [Flynn] did anything wrong.’ ”

Somewhere in this chain of events, something went horribly wrong. One possibility is that Yates, having secured Comey’s approval to brief McGahn based on Flynn’s false statements to the FBI agents, didn’t mention those statements to McGahn. Another possibility is that McGahn, having received at least a strong signal from Yates that Flynn had misled the FBI, didn’t tell Trump. A third possibility is that McGahn told Trump, and Trump didn’t care. One of these scenarios must be true. To find out, we need to put these people, and perhaps those around them, under oath.