Whatever its larger meaning or impact, Representative Joseph Crowley’s stunning loss to Alexandria Ocasio-Cortez in last Tuesday’s primary election already has set off one tremor within the Democratic Party: It has thrown House leadership into chaos.

Mr. Crowley is chairman of the Democratic caucus, making him the fourth-ranking Democrat in the House. He also was the heir apparent to the minority leader, Nancy Pelosi. Ms. Pelosi, now 78, has herded Democratic cats for nearly 16 years and has made clear her desire to stay put if the party wins back the majority in November. But she’s expected to face a serious challenge to her rule after the election, whether or not the party reclaims the majority. A swelling segment of Ms. Pelosi’s caucus — especially younger lawmakers — feel it is time for a change, and at least 20 Democratic candidates have pledged not to support her for leader if they win their races or have called for a change in leadership.

But with the loss of Mr. Crowley, who was a relative young ’un in the Democratic leadership, at age 56, House Democrats have nothing even approaching a backup plan. This has set off a fresh round of hand-wringing and squabbling — privately, if not publicly — about when a new generation will get a chance to lead, and who should be the face of that leadership. This is hardly a useful distraction during a high-stakes election year. But it’s a situation for which Ms. Pelosi has only herself to blame.

For too long, this regime has clung to power at the expense of future leaders. Neither of Ms. Pelosi’s two chief deputies, Steny Hoyer, the party whip, and Jim Clyburn, the assistant leader, is a remotely viable successor. Like Ms. Pelosi, both men are just shy of 80 and have occupied top-tier posts for over a decade. At this point, the caucus leadership has gone from stale to downright ossified.