Now, compare the political outcomes. The broad, bipartisan vote against Nixon led over time to a series of events in which conservatives, including the Republican candidate who preceded Nixon, Senator Barry Goldwater, abandoned the president, who ultimately resigned. The narrow, partisan votes against Mr. Clinton led to his acquittal. Al Gore narrowly lost the next presidential election while Democrats picked up a seat in the House. Hillary Clinton went on to become a senator, secretary of State and presidential nominee. In other words, when Republicans allowed their animus against Mr. Clinton to override their political instincts, they were hurt, but the Clintons were not.

Surely Ms. Pelosi must know that there are not 67 votes in the Senate to convict President Trump of anything relating to his phone call with President Zelensky. So it’s just political theater. The problem is that as it plays out over the next year, everyone will get the joke: The House is just going through the motions to stoke its own base before the election, just as Newt Gingrich’s majority did in 1998. That, in turn, will energize Republicans to support the president. But there is another danger for Democrats lurking here: that they will ultimately demoralize their most loyal voters when they realize the joke’s on them. There will be no resignation, there will be no conviction in the Senate.

But there will be an election. And by focusing on their obsession with the person of Donald Trump, Democrats are giving up the opportunity to talk about wages, employment, the shrinking middle class or any of the other things that motivate normal voters.