This is what could happen if McCarthy falls short.

Because it is so rare for a speaker election to require more than one vote, there is little modern precedent to govern the chaos that could ensue if Kevin McCarthy, the Republican leader, fails to win the speaker’s gavel on the first ballot.

But there are a few clear-cut options available to lawmakers.

Mr. McCarthy and his allies would most likely begin horse-trading with rebel lawmakers on the House floor or in the cloakroom to try to win their support. Some Republicans have privately noted that it could become obvious more quickly than usual if Mr. McCarthy will fall short on the first ballot, because a number of lawmakers who have vowed to oppose him will be called on early in the alphabetical vote.

At the same time, other lawmakers could try to run as potential consensus candidates. Or Republican rank-and-file members might try to draft one of their colleagues into running if it appears that no amount of cajoling will win Mr. McCarthy the votes he needs.

A lawmaker could offer a resolution to the election process, such as lowering the vote threshold needed to become speaker and endorsing a plurality winner.

Lawmakers might also try to take a break from voting and put forward a motion to adjourn. That would require the approval of a majority of the House: 218 votes.

Unless they move to adjourn, lawmakers will have to keep voting until a speaker is elected.