Americans love a good political brawl, and that’s terrible news for Speaker Nancy Pelosi. Her Democratic Party has commenced a full throw-down—with itself.

Few things have benefited Democrats more in the past few years than the Donald Trump show. The president likes to be the center of attention, and the media likes nothing more than to oblige him. This dynamic helped make the 2018 election a referendum on the man himself rather than his policies, and that made Mrs. Pelosi speaker of the House.

Democrats envisioned the same dynamic helping them win the White House in 2020. Mrs. Pelosi has been to that rodeo before, after the 2006 election, when she was first elected speaker. She mobilized her committee chairmen to launch focused investigations to keep the spotlight on George W. Bush’s Iraq war, energy policy, detainee treatment, etc. She corralled a diverse caucus to pass a modest agenda, “Six in ’06,” that showed Democrats could get things done but didn’t put them in the limelight, much less make them look crazy. This paved the way to the election of Barack Obama in 2008, and Democrats figured Mr. Trump would make a repeat even easier.

Instead, Mrs. Pelosi this week accomplished the remarkable feat of sidelining Mr. Trump and owning most of the unpleasant headlines herself. House Judiciary Chairman Jerry Nadler explained that his sprawling Trump investigation was primarily designed to convince voters that Democrats were “not just trying to steal the last—to reverse the results of the last election.” This required his colleagues to deny furiously that the party has already decided on impeachment.

Then there was the crackup between House party elders who wanted Democrats to condemn the anti-Semitism of Rep. Ilhan Omar, and woke freshmen who wanted to turn smears against Jews into a fuzzy discussion of hurt feelings. Members battled for days, only for Mrs. Pelosi on Thursday to roll over to the progressive left’s demand that any resolution condemn “hate” in general and not anti-Semitism specifically. Even CNN described all this as “chaos.”