Then came the House Judiciary Committee hearings on impeachment in 1974. Its final deliberations weren’t a trial, but according to the Langs, viewers experienced them that way, so that public debate came to revolve around the question of Nixon’s guilt or innocence. On Aug. 5, definitive proof of his guilt emerged: the “smoking gun” recording of Nixon agreeing to a plan to have the C.I.A. ask the F.B.I. to stop investigating Watergate. After that, wrote the Langs, “the inexorable logic of the facts” led to the president’s downfall.

We are about to find out whether facts still have an inexorable logic. The outlines of Donald Trump’s venality and fundamental civic disloyalty have been obvious since the 2016 campaign; Hillary Clinton warned us about him just as McGovern had warned about Nixon. But so far, neither Democrats nor prosecutors have woven the various threads of presidential wrongdoing into a coherent picture, showing how Trump’s shady business practices, opaque finances, vulnerability to blackmail, abuses of power and subservience to foreign autocrats all intersect.

Now, however, Democrats have begun a full-spectrum public investigation of the president. Michael Cohen’s blockbuster testimony before the House Oversight Committee last week was just an opener.

On Monday, the House Judiciary Committee took the first steps in an inquiry into obstruction of justice, public corruption and abuses of power by the Trump administration. In an operatic legal fusillade, it sent document requests to 81 people and entities, including Donald Trump Jr., Jared Kushner, the National Rifle Association and Allen Weisselberg, the chief financial officer of the Trump Organization. They have two weeks to respond. (Ivanka Trump is not on the list, but the requests that went out call for numerous documents about her, and the committee has said that more requests could be forthcoming.)

“To me it’s a thrilling moment,” Jamie Raskin, a Democrat on the House Judiciary Committee, told me. Finally, he said, “we have an opportunity to discover what has been happening in our country over the last two years and several months.”