What the history of House speaker elections tells us about 2019

Washington (CNN)When lawmakers in the House of Representatives vote to elect their next speaker on Thursday, Democrat Nancy Pelosi is almost guaranteed to win.

But if even a few Democrats vote against her it will follow a trend that started just a few years ago, with tea party opposition to former Republican House Speaker John Boehner of Ohio.
    Until a few fellow Republicans broke with their party to oppose Boehner's speakership in 2013, there had been virtually no cases of majority-party dissent in speaker nominees' bids in modern history. In fact, for 70 years, from 1925 to 1995, zero majority-party House members took to the floor to oppose their party's nominee for speaker. Not so today. Pelosi was able to unify the vast majority of her party behind her, but a few fellow Democrats have said they will oppose her.
    A strong two-party system, plus a willingness to defer to closed-door caucus meeting votes, had unified parties on the floor for decades. Not anymore. Votes for the House speaker have become publicly contentious. Following the votes against Boehner, some Republican members started to use votes on the floor as an instrument to try to effect change or make symbolic gestures of ideological rebuke that later play out on the campaign trail.
    Two dozen members strayed from Boehner in 2015. He went on to retire later that year. But for Democrats, the opposition Pelosi is facing is a first. Any rogue votes by House Democrats on the floor would be the first stray speaker votes from a majority-Democratic caucus in at least a century.
    "You've got a lot of new members that have been elected on the far left and far right who don't accept this norm that you're supposed to follow the organizational cartel and vote with your party," said Matthew Green, a professor at the Catholic University of America who specializes in the modern House speakership. "Speakers are very public figures now, and they become unpopular."
    There are also Democratic members from more moderate districts looking to oppose Pelosi from the right. "They're having to appeal to some constituents who are not ideological warriors -- and bashing Nancy Pelosi is a way to show you're not an ideological warrior," explained Charles Stewart, a professor at the Massachusetts Institute of Technology who focuses on Congress and elections.
    In the immediate aftermath of the 2018 elections, Pelosi has faced opposition from more than enough members to threaten her path to a majority on the House floor. But through savvy negotiations and concessions she has reduced the opposition to just a few scattered voices.
    Some prominent potential opponents, like Reps. Seth Moulton of Massachusetts and Tim Ryan of Ohio, struck a deal in mid-December to support Pelosi after she backed a term-limit deal for House leadership. Rep. Marcia Fudge of Ohio also decided not to challenge Pelosi after she was handed control of a House subcommittee on elections.
    The strategy Pelosi employed to garner support ahead of Thursday's vote has parall