Traditionally, a norm has existed in both parties that all members support their party nominee when the vote goes to the House floor. That is, even if the vote in the caucus is 130-110, the 110 who did not vote for the nominee are expected to back them on the House floor. From 1947 until 1997, there was not a single defection from this norm. In recent years, however, a small number of members of both parties have defected from their party nominee. In 2011, 18 votes went to candidates other than the party nominees. In 2013, 14 votes did. In 2015, 28 did. In 2017, 5 did. In none of these cases did the votes comprise the balance of power such that they could deny the election to the majority party’s candidate. In several of the elections, however, a faction of conservative Republicans explicitly sought to use the floor vote to deny their party’s nominee the Speakership.This time, a faction of Democrats is threatening not to support Nancy Pelosi.
Many observers believe that a commitment by Pelosi or other current leaders to step down in the near future might satisfy the insurgents; the current top Democratic leadership has been in place for 16 years, and there is definitely some general caucus dissatisfaction related to the inability of members to move up the leadership ladder. Alternatively, Pelosi might threaten to punish members who vote against her on the floor; rule 34 of the Democratic caucus binds members to vote for the nominee. When two members of the GOP leadership voted against Speaker Boehner in 2015, he immediately removed them from the Rules Committee.
If bargaining fails, Pelosi could call the insurgents’ bluff, and simply win the nomination in the caucus and go to the floor with it, daring them to deny her the Speakership. Similarly, she could lean on some of them to vote “present” on the floor, rather than for a different candidate. Under current House rules, nominees need a majority of those voting “for a person by name” to win the Speakership. If anyone votes “present,” the total number of votes is reduced by 1, meaning that for every 2 people who vote “present,” the threshold needed to win reduces by 1 vote. If Pelosi could convince 10 Democrat insurgents to vote “present,” she would only need 213 votes, which would neutralize the balance of power held by the holdout insurgents.
Tactically, Pelosi could also employ the help of Republicans, though relying on them to sustain her Speakership would be a dangerous (and highly unlikely) move. Republicans could outright vote for her for Speaker to make her majority, or they could vote “present” to reduce the majority threshold. They could also vote in favor of a resolution declaring that the Speakership be decided on a plurality basis; this broke the Speakership deadlocks in both 1849 and 1856. But again, all of these possibilities are highly unlikely.