WASHINGTON — What if House Democrats tried to stage a coup and nobody showed up?

That is the predicament facing Democrats as a quiet rebellion simmers in their ranks to block Representative Nancy Pelosi of California from being speaker. Inside the Capitol and at nearby watering holes and restaurants, there are hopeful whispers among a small band of Democrats that a fresh-faced new leader will come forward to challenge Ms. Pelosi, who has led House Democrats for 15 years.

But so far, no one has emerged to take her on. As much as some House Democrats, including several among the wave of newcomers elected this month, say they want to shake up a calcified party leadership, would-be challengers are keenly aware of the immense power Ms. Pelosi wields, and fearful of institutional retribution and reputational damage if they step forward to test the status quo.

Democrats who had hoped to release a letter clearly demonstrating that Ms. Pelosi did not have the votes to become speaker pulled back on Friday, hoping to garner more than the 17 signatures that they said they had collected. Representative Marcia L. Fudge of Ohio, who is considering a run against Ms. Pelosi, said she was still undecided.

And Ms. Pelosi, a legendary legislator, vote-counter, campaigner and fund-raiser who served as speaker from 2007 to 2011, has expressed supreme confidence that she will be elected again in January. She has enlisted powerful allies to weigh in on her behalf and worked to build an air of inevitability around her bid, including through a letter of support circulated by a veteran lawmaker, Representative Nita M. Lowey of New York, and signed by 61 Democratic women as of Friday afternoon. (An additional four women elected this month have since said publicly that they will back her.)