Evidently, F.B.I. counterintelligence agents were alarmed when they read the wiretap transcripts of Mr. Flynn’s Christmastime chats with the Russian ambassador. He appeared to reassure the Kremlin not to worry about the Obama administration’s sanctions, and that once Mr. Trump was in office and Mr. Flynn took over at the N.S.C., the nerve center for secret intelligence at the White House, things would be better for the Russians.

After President Trump was sworn in on Jan. 20, Mr. Comey pondered the possibility that the Russians could blackmail the new national security adviser. He took his concerns to his immediate superior — the acting attorney general of the United States, Sally Yates — and she, in turn, went directly to the White House and relayed that warning. You remember Sally Yates. President Trump fired her on Jan. 30. Now he has had to fire Mr. Flynn.

We know that Mr. Flynn has had some troubles with the truth before. He became infamous while running the Defense Intelligence Agency from 2012 to 2014 for what his subordinates called “Flynn facts” — statements with a shaky basis in reality. He has lied to superiors, including Vice President Pence, more than once, in particular about his talks with Moscow’s man in Washington.

And we now know that F.B.I. agents interviewed Mr. Flynn about those same talks shortly after Inauguration Day. Lying to the F.B.I. is punishable by five years in prison. Mr. Flynn may be guilty of no crime beyond bad judgment. But this case is no longer about him and his relationship with the truth. The bureau wants to know whether members of the Trump campaign were in cahoots with the Kremlin in a covert crusade on behalf of their candidate, and so does Senator McCain.

Meanwhile, the president is preoccupied with another issue. “The real story here is why are there so many illegal leaks coming out of Washington?” he tweeted on Tuesday.

It’s been a long time, but remember this: The road to Watergate and the resignation of Richard Nixon began in April 1969, three months after his inauguration, when the president ordered Mr. Kissinger to wiretap members of his own staff in an effort to stop embarrassing leaks of secret information. One thing led to another until the commander in chief was athwart the Constitution.

It’s been barely three weeks since the Trump team took office, and a distinct aroma has started wafting out of Washington, what Mr. Kissinger is said to have called “the odious smell of truth.”