It is becoming increasingly clear that the Republican party is headed toward a contested convention. The likelihood of a loss by Donald Trump in Wisconsin next week would still leave him far ahead of his competitors in delegate count, but would diminish the already slim chance he has of arriving at the convention with an absolute majority. The party would then have to choose between nominating Trump (who has won most primaries but has yet to take an absolute majority in any state), or blocking him by turning to a candidate like Ted Cruz, who has been even less popular among Republican voters.
Regardless of which choice the convention makes, someone will walk out. If Trump gets the nomination, important elements of the party establishment will refuse to support him, and there are enough Republican voters who would sit on their hands to cost him some swing states. Given that most polls show him losing to either Hillary Clinton or Bernie Sanders already, the prospect of losing a significant part of the GOP coalition just enhances the prospect of defeat.
On the other hand, if Trump is denied the nomination, he is highly likely not only to walk out, but to stage an independent campaign. His prospects of victory would be very poor, but he might very well outpoll the official GOP nominee, just as Teddy Roosevelt did with his Bull Moose campaign of 1912. He currently has 40-45 percent of Republican voters; if he took 30 percent of GOP voters with him, and added some fraction of independents and Democrats, he could easily take a quarter of the national vote in November, leaving the Republican nominee with about 20 percent, and the Democrat with 55.
If Trump is denied the nomination and walks out with a large chunk of his followers, what will be left without Trump is a rump, competitive only in the most conservative states and districts.
Trump’s voters are a very distinctive subset of Republican voters: they are overwhelmingly white, disproportionately male, less educated, with lower incomes. They have provided the votes to make the party nationally competitive at least since Reagan’s election in 1980, but they feel that the party has done little for them as it has served the interests of the big corporations. Trump could easily take many of them with him when he walks.
This looks like an almost certain disaster for the GOP at the presidential level, which is ironic given that the most likely Democratic nominee would be Hillary Clinton, who is also viewed negatively by nearly half of the electorate, largely as a result of a quarter century of relentless Republican efforts to blacken her name. This would be a classic case of snatching defeat from the jaws of victory.
The Republican Party was forged in the crucible of the crisis that led to the Civil War. It rose from the ashes of the Whigs (Lincoln was a Whig before he was a Republican). The larger issue is whether the impending split in the Republican Party sends it to follow the Whigs into oblivion, or whether it can instead regroup. Much depends on what happens in the congressional and senatorial elections. In 1856, the Whigs were moribund and the Republicans elected a significant minority to Congress. In 1912, the Republicans, even while coming in third in the presidential election, vastly outnumbered Roosevelt supporters in Congress.
Already, congressional Republicans are taking steps to insulate their candidates from Trump, by localizing their campaigns, in hopes that they can survive a massive Trump defeat. There is no sign that Trump will attempt to put up a significant number of supporters as congressional or senatorial candidates. The likelihood, then, is that the GOP will lose seats in both houses, will probably lose the Senate majority, might lose the House majority, but the party will survive.
But the self-inflicted damage will take a long time to repair. The Trump voters are some significant portion of the Tea Party wave that started in 2010. If Trump is nominated and they take over the party, a big chunk of ideological and social conservatives (Cruz supporters among others), as well as moderates, may look for another home, especially if Trump loses in November. Many moderates could continue the process of migration to the Democrats. The conservatives could form their own, ideologically pure conservative party.
If Trump is denied the nomination and walks out with a large chunk of his followers, what will be left without Trump is a rump, competitive only in the most conservative states and districts. And while Trump does not seem inclined to build his own party, some of his supporters might. It could look something like the French National Front, and it could pose a significant challenge to the GOP.