CNN — The 119th Congress will begin on Friday, ushering in a new era of Republican control in Washington that will start with a high-stakes leadership fight to pick the next House speaker. Mike Johnson is vying to retain the gavel and has President-elect Donald Trump’s endorsement, but he faces tough vote math with the narrowest House majority in nearly 100 years, leaving little room for error. Johnson can only afford a single GOP defection if every lawmaker shows up and votes, and one House Republican - Rep. Thomas Massie of Kentucky - has already said he won’t vote for him, while roughly a dozen more have not committed to supporting him. Looming over the race is the question of what happens if the House has not yet elected a speaker by Monday, January 6, the day lawmakers are supposed to count electoral votes and finalize the results of the presidential election – a scenario that would put Congress into unprecedented territory. How many votes Johnson needs to win To be elected speaker, a candidate must win a majority of votes out of all votes cast. If all 435 members of the House vote, then a majority is 218 votes. There is expected to be one vacancy when the House convenes for the vote. Former GOP Rep. Matt Gaetz of Florida has said he won’t take the seat he was elected to in the new Congress. That leaves 434 members with 219 Republicans and 215 Democrats. If all 434 vote, it takes 218 to win. Members can vote for anyone they want There’s no rule that the speaker must be a House member. Members can vote for anyone, regardless of if the name was put into nomination or if the individual is a member of the House. Members can also effectively abstain from voting at all by simply saying “present” when they are called on to vote. The vast majority of lawmakers, however, will vote for their party’s leader. It doesn’t always require 218 votes While 218 is typically thought of as the magic number, it’s possible to be el Before voting can start, candidates must be nominated. GOP Rep. Lisa McClain of Michigan is expected to give a nominating speech for Johnson, and Democratic Rep. Pete Aguilar of California is expected to give a nominating speech for House Democratic leader Hakeem Jeffries. But any member can nominate anyone, so additional candidates could be nominated. During the vote, a clerk will call on members by name in alphabetical order and each will have the chance to say which candidate they support. This is also when members could opt to say “present” instead of voting for a candidate. At the end, any members who did not vote will be given the opportunity to do so, and if any member wants to change their vote, they can. There could be a floor fight with multiple rounds of voting Johnson’s allies are projecting confidence he’ll be able to secure the speakership, but even they are bracing for the possibility that it could go into multiple rounds of voting, leading to a drawn-out floor fight.