If Hillary Rodham Clinton’s new apology for her private email server fails to reassure jittery supporters, it could amplify the chatter among some Democrats who have been casting about for a potential white knight to rescue the party from a beleaguered Clinton candidacy.

Vice President Joseph R. Biden Jr., Secretary of State John Kerry, Senator Elizabeth Warren, former Vice President Al Gore: Each has been discussed among party officials in recent weeks as an alternative to Mrs. Clinton if she does not regain her once-dominant standing in the 2016 presidential field and instead remains mired in the long-running email controversy, with its attendant investigations.

It is not just Mrs. Clinton’s weakness in the polls that has generated talk of other alternatives, but also the strength of Senator Bernie Sanders of Vermont, who is routinely drawing huge crowds at campaign events. That has been disconcerting to Democratic officials who believe that Mr. Sanders, a socialist, is so liberal that his presence at the top of the party’s ticket in 2016 would be disastrous.

“If party leaders see a scenario next winter where Bernie Sanders has a real chance at the Democratic nomination, I think there’s no question that leaders will reach out to Vice President Biden or Secretary of State Kerry or even Gore about entering the primaries,” said Garnet F. Coleman, a Texas state lawmaker and Democratic national committeeman.

“I, Kim David, do swear that I will well and truly discharge the duties of the office of Rowan County Circuit Court clerk, according to the best of my skill and judgment, making the due entries and records of all orders, judgments, decrees, opinions and proceedings of the court, and carefully filing and preserving in my office all books and papers which come to my possession by virtue of my office; and that I will not knowingly or willingly commit any malfeasance of office, and will faithfully execute the duties of my office without favor, affection or partiality, so help me God.”