Look for the next several months to be a nonstop pageant of subpoenas, hearings and court challenges.

Mr. Nadler’s panel is not alone in looking to impose accountability on a devious and dishonest president. But his investigation is special in at least one regard. As students of Congress — or of presidential scandals — can tell you, the House Judiciary Committee is where impeachment proceedings are born. And the areas on which Mr. Nadler will focus — obstruction of justice, public corruption and abuse of power — are precisely the sorts of high crimes and misdemeanors on which such cases are built.

Not that Mr. Nadler is raring to impeach. Many Democrats worry that an attempt to remove the president could prompt a political backlash, and no one wants to repeat what happened in 1998, when House Republicans’ obsessive pursuit of President Bill Clinton contributed to the party taking an electoral beating.

Even as he prepared to start this investigation, Mr. Nadler sought to tamp down expectations. “Impeachment is a long way down the road,” he said Sunday in an ABC News interview.

Political investigations tend to be marathons rather than sprints, requiring the slow, meticulous accretion of evidential layers. It’s easy to forget how slowly and painfully the Watergate investigation unfolded. It was more than a year after John Dean’s congressional testimony that President Richard Nixon resigned. With his investigation, Mr. Nadler is looking to build a case for impeachment so compelling that it will have enough bipartisan support to survive the Republican-controlled Senate. Barring that, his investigation will serve to keep the heat on Mr. Trump, and perhaps keep the Democratic base at least somewhat placated, as the next election approaches.