President Trump may have thought the departure of his national security adviser, Michael Flynn, would end the controversy over his administration’s involvement with Russia, but the damning revelations keep coming. The whole fiasco underscores the dysfunction and dishonesty of his White House and how ill prepared it is to protect the nation.

It’s unlikely that Mr. Flynn would have been pushed out absent a revelation on Monday by The Washington Post: that the Justice Department told the White House in January that Mr. Flynn had misled senior officials about a phone call with the Russian ambassador. Justice told the White House that, contrary to his claims, Mr. Flynn had discussed American sanctions against Russia with the ambassador. The discrepancy between what Mr. Flynn had said publicly and what the Russians (and American intelligence officials) knew made Mr. Flynn vulnerable to Russian blackmail. But the White House evidently didn’t feel the need to act on that danger as long as it was concealed from the public.

On Tuesday, the White House admitted that Mr. Trump was told more than two weeks ago about Mr. Flynn’s deception, even though the president told reporters on Friday that he was unaware of a news report to that effect. Mr. Flynn, a hothead and an ideologue, was not fit to be national security adviser in the first place. That Mr. Trump clung to such a compromised person in such a sensitive position is at best an abysmal failure of judgment. As late as Monday, Mr. Flynn was in security briefings and had access to the president.

In his resignation letter, Mr. Flynn said he had given senior officials “incomplete information” about the phone call. F.B.I. agents interviewed Mr. Flynn days after the inauguration on that same subject, The Times reported on Tuesday. That means he could be exposed to a felony charge if he lied to them as well. The Times also reported Tuesday that current and former American officials said other Trump associates and campaign officials had had repeated contacts with senior Russian intelligence officials in the year before the election.