Since Republicans and Democrats began holding presidential primaries there have been six occasions in which the candidate receiving the most primary support did not go on to receive his party’s nomination. In five of these instances the nominee lost during the general. The only winner was Warren G. Harding in 1920 when both parties nominated the loser of their presidential primary contests.    

Until the beginning of the last century political bosses controlled the delegates who selected each party’s presidential candidate. The process was undemocratic, subject to corruption, and lacked transparency. But because the Constitution does not specify a way in which parties must select their eventual nominees, each determined its own rules for how their standard bearer was chosen.

The 1912 presidential election was the first to see delegates apportioned based on voter choice when 12 of 48 states held primary contests. This number fluctuated over the years but essentially remained the same. More than half a century later there were still only a dozen states holding primaries.  

All this changed after the tumultuous 1968 Democratic National Convention in Chicago when Hubert Humphrey, who entered the race late and did not participate in a single primary, was selected as the Democratic nominee. Humphrey, who would later lose to Richard Nixon, was the sitting Vice President and widely believed to have secured his party’s nomination due the machinations of party bosses like Chicago Mayor Richard Daley and then President Lyndon Johnson.

The defeat led to the creation of the McGovern-Fraser Commission and a major reassessment of the Democratic party’s nominating rules and procedures. The result was the elimination of the secret appointment of delegates and the awarding of a large proportion to individual candidates based on how well they did in each state’s primary or caucus. Republicans quickly followed the Democrats’ lead albeit with a few differences, (i.e. the GOP has no “superdelegates”), and today 46 states conduct presidential primaries with four holding party-run caucuses. Beginning with the 1972 election no nominee has been selected without first winning at least a plurality of support from their party’s primary voters.

Since Donald Trump solidified his frontrunner status the GOP establishment has been trying to figure out ways to prevent him from becoming the nominee. Because it appears too late to stop Trump by consolidating around another candidate, the favored approach is to keep him from winning the 1,237 delegates needed to achieve a majority, and hence, a lock on the nomination. In this scenario Republican convention delegates, who are required to support the candidate to whom they are pledged in the first round of voting, may be cajoled or pressured into switching to another nominee in subsequent ballots, thereby thwarting Trump.      

Romney endorsed this exact strategy before the Republican debate last Thursday when he chose not to support a specific candidate but instead encouraged everyone to get behind whoever happens to be the leading non-Trump candidate in their respective states. The GOP establishment likely intends to chip away at Trump’s poll numbers hoping by the time everyone makes it to Cleveland in July his support will have dwindled to the point where another candidate may have a shot at the nomination in what would end up being a brokered convention.

There are legitimate reasons why the Republicans may not want Donald Trump as its nominee. But if they want to reclaim the White House and if Trump continues to win a plurality of primary voters, then the smart thing would be for him to receive the nomination, even if he is unable to secure the required majority on the first ballot. Whether the GOP establishment likes Trump or not, he is increasingly becoming their best chance of winning in November.   

One major reason for this is a candidate’s performance during the primaries indicates how well he or she will do in November. Writing in the America Political Science Association’s January 2013 post-election edition of PS: Political Science and Politics, Professor Helmut Norpoth of Stony Brook argues that not only do primary performances matter when forecasting the general, but since 1952 the state which is best predictor of who will ultimately win is New Hampshire where Donald Trump won 35 percent of the vote while competing against eight other candidates. Hillary Clinton secured slightly more with 38 percent, but lost to Bernie Sanders who came away with 60 percent. This gives Trump the edge, says Norpoth, whose model is based on the proportion of the vote a candidate receives relative to his or her strongest competitor, and which correctly predicts the winner of every presidential election going back to 1912 with the exception of 1960. He says Trump would likely win in a matchup against either Clinton or Sanders while both Cruz and Rubio would lose.  

History also indicates rallying behind Trump may be a good idea insofar as winning is concerned. As noted earlier, since primary contests began the nominee was someone not chosen by their party’s primary voters, that candidate lost 83 percent of the time. If we eliminate the 1920 election when neither candidate was preferred choice of the party faithful, then statistically speaking, there is a 100 percent chance choosing another candidate will mean defeat in the general. Past results are certainly no guarantee of future outcomes and anything may happen, just as this year’s unusual primary season has proven with Trump’s electoral victories, yet they are suggestive.

There’s also the fact the party with an incumbent coming off two consecutive terms in office tends to lose. Six out of seven times since World War II an incumbent party was denied a third term in office, the exception being George H.W. Bush in 1988. (Al Gore did win the popular vote in 2000 but not enough states to win the electoral college.) And since the start of the two-party system in 1828, only twice have Democrats gone on to secure more than two consecutive terms, the last being Franklin Roosevelt in 1940 and the other in 1836. The sample size is small and as Nate Silver notes, the White House is not a metronome, but the historical trend is clear. Whether it continues is anyone’s guess.

But perhaps the most important reason to support Trump is if he ends up having the nomination pulled out from under him despite being the preferred choice of a plurality of Republican primary voters, then it will send a clear message to the rank and file their preferences do not matter to the establishment, something many of them believe already. It’s one thing to play the game and lose but then go on to support your party’s nominee when they win fair and square. It’s quite another when your man lost and your vote was dismissed due to political chicanery.

This brings up a final, far more dangerous possibility for Republicans seeking a contested convention. If Trump can legitimately claim to deserve the nomination but does not receive it, then he will undoubtedly turn the November election into a three-way race. An exodus of party members would follow, despite appeals to unite behind whoever becomes the compromise candidate and Trump would likely pick up a number of independents and disaffected Democrats. Republicans have been claiming Trump is unelectable in the general, and whether that’s true or not is up for debate, but the fact is a third party Trump candidacy would almost certainly guarantee a Democratic victory.

This is exactly what happened in 1912. Teddy Roosevelt won the vote of the people in states hosting Republican primaries, but at the convention party bosses decided to instead run with Howard Taft. An angry Roosevelt collected his supporters and walked out. They next day he started the short-lived Progressive Party (otherwise known as the “Bull Moose”), and ran his own ticket. Taft ended up not just losing in the general to Woodrow Wilson, but actually came in third place behind Roosevelt. The collective share of Taft’s and Roosevelt’s votes, however, was enough for the Republicans to have won had they united under a single ticket.

In last Thursday’s debate all of the remaining candidates pledged to support the eventual “nominee.” They should go a step further and pledge to support the expressed will of Republican primary voters.  Anything less would mean a loss this November.