LAST week reports emerged that lawyers for Michael Flynn, Donald Trump’s former national-security advisor, had stopped speaking to Mr Trump’s legal team—hinting that Mr Flynn was negotiating a deal with Robert Mueller’s team of special prosecutors. On the morning of December 1st the other shoe dropped: in a federal court in Washington, DC Mr Flynn pleaded guilty to one count of making false statements to FBI agents; the crime carries a maximum penalty of five years imprisonment. He was, he said, co-operating with the investigation, a decision he had taken, “in the best interests of my family and of our country.”

Mr Flynn lasted just 24 days as national-security advisor; he resigned after admitting that he lied to White House officials about conversations with Russia’s ambassador. He joined Mr Trump’s campaign early, enthusiastically leading crowds to chant “Lock her up!” (referring to his opponent, Hillary Clinton) on the campaign trail, even as he was engaging in lobbying work for Turkish interests, apparently without the White House’s knowledge.

Mr Flynn amassed a stellar reputation as an intelligence agent, when he had a defined mission to carry out. As head of the Defence Intelligence Agency, a position to which Barack Obama appointed him in 2012 and from which he was fired in 2014, he was reportedly abusive, erratic and prone to say things that were not true (his staff called them “Flynn facts”).

Mr Flynn also received $65,000 from three Russian firms, including RT, a television network, in connection with a speech-making trip he took to Moscow in 2015. He failed to disclose the trip or income on his security-clearance forms; the payment also violated rules against retired military personnel receiving money from foreign governments without permission.

He is the fourth—and most senior—figure from the Trump campaign to be charged. George Papadopoulos, a foreign-policy advisor to the campaign, pleaded guilty to the same charge Mr Flynn faces, while Paul Manafort and Rick Gates, Mr Trump’s former campaign manager and his business associate, remain under house arrest, charged with money laundering and failing to register as foreign agents.

But unlike Messrs Manafort and Gates, who were charged with crimes predating their involvement with the campaign, Mr Flynn committed the crime to which he pleaded guilty while working in the White House. On January 24th, just four days after Mr Trump took office, Mr Flynn told investigators that he did not ask Russia’s ambassador, one month earlier, to refrain from responding to recently imposed sanctions. In fact, he had called the ambassador in December after talking with unnamed “Presidential transition team officials”—before Mr Trump became president. He also lied about discussing a United Nations vote with the ambassador. Mr Flynn shared with Mr Trump an obsession with Islam, with which he seemed to believe America is locked in a massive civilisational conflict. This drew him to Mr Trump’s campaign, and afterward to Russia, which he saw as an ally in that fight. But Mr Trump was not yet in office when Mr Flynn had these conversations; he was, in effect, undermining his own government’s foreign policy, which the Logan Act forbids.

Mr Mueller’s team reportedly had been looking into a variety of allegations surrounding Mr Flynn, including failing to register as a foreign agent and a supposed plot to forcibly remove a Turkish national living in Pennsylvania and send him back to Turkey. The single-count perjury indictment, a much lighter charge than Mr Flynn might have expected, seems to suggest that he has agreed to provide information to Mr Mueller. The plea presumably leaves Mr Mueller with ample leverage if Mr Flynn’s co-operation stalls: he can always bring more charges, perhaps in concert with a state attorney-general, which would put Mr Flynn beyond Mr Trump’s pardon power (the president can only pardon federal crimes).

That should make Mr Trump nervous. Yesterday, the New York Times reported that Mr Trump had been trying to get Republican senators to end the Senate Intelligence Committee’s investigation into alleged Russian meddling in the 2016 election. And earlier this year Mr Trump fired James Comey as FBI director after trying to pressure him to “let go” of his investigation into Mr Flynn. Now Mr Flynn, whom Mr Trump repeatedly defended, is a felon, and the investigation—far from being wound down by year’s end, as Mr Trump hoped—looks set to continue.

Correction (December 4th, 2017): This piece has been amended to remove a reference to an erroneous report from ABC news.