If Donald Trump wins the Republican presidential nomination, he’ll have undermined a lot of assumptions we once held about the GOP. He’ll have become the nominee despite neither being reliably conservative nor being very electable, supposedly the two things Republicans care most about. He’ll have done it with very little support from “party elites” (although with some recent exceptions like Chris Christie). He’ll have attacked the Republican Party’s three previous candidates — Mitt Romney, John McCain and George W. Bush — without many consequences. If a Trump nomination happens, it will imply that the Republican Party has been weakened and is perhaps even on the brink of failure, unable to coordinate on a plan to stop Trump despite the existential threat he poses to it.

Major partisan realignments do happen in America — on average about once every 40 years. The last one, which involved the unwinding of the New Deal coalition between Northern and Southern Democrats, is variously dated as having occurred in 1968, 1972 and 1980. There are also a lot of false alarms, elections described as realignments that turn out not to be. This time, we really might be in the midst of one. It’s almost impossible to reconcile this year’s Republican nomination contest with anyone’s notion of “politics as usual.”

If a realignment is underway, then it poses a big empirical challenge. Presidential elections already suffer from the problem of small sample sizes — one reason a lot of people, certainly including us, shouldn’t have been so dismissive of Trump’s chances early on. Elections held in the midst of political realignments are even rarer, however. The rules of the old regime — the American political party system circa 1980 through 2012 — might not apply in the new one. And yet, it’s those elections that inform both the conventional wisdom and statistical models of American political behavior.

This doesn’t necessarily mean we’ll be completely in the dark. For one thing, the polls — although there’s reason to be concerned about their condition in the long-term — have been reasonably accurate so far in the primaries. And some of the old rules will still apply. It’s probably fair to guess that Pennsylvania and Ohio will vote similarly, for example.

Still, one should be careful about one’s assumptions. For instance, the assumption that the parties will rally behind their respective nominees may or may not be reliable. True, recent elections have had very little voting across party lines: 93 percent of Republicans who voted in 2012 supported Romney, for example, despite complaints from the base that he was insufficiently conservative. And in November 2008, some 89 percent of Democrats who voted supported Barack Obama after his long battle with Hillary Clinton.

But we may be entering a new era, and through the broader sweep of American history, there’s sometimes been quite a bit of voting across party lines. The table below reflects, in each election since 1952, what share of a party’s voters voted against their party’s presidential candidate (e.g., a Democrat voting Republican or for a third-party ticket). There’s a lot of fascinating political history embedded in the table, but one theme is that divisive nominations have consequences.

ELECTION DEMOCRATS REPUBLICANS 1952 23% 8% 1956 15 4 1960 16 5 1964 13 20 1968 26 14 1972 33 5 1976 20 11 1980 33 15 1984 26 7 1988 17 8 1992 23 27 1996 15 19 2000 13 9 2004 11 7 2008 11 10 2012 8 7 Share of party’s voters voting against its presidential candidate Sources: Gallup (1952-1972), National Exit Polls (1976-2012)

In 1972, for instance, about a third of Democrats voted for Richard Nixon rather than George McGovern, who won the Democratic nomination despite getting only about a quarter of the popular vote during the primaries. The Democrats’ tumultuous nomination process in 1968 was nearly as bad, with many defections to both Nixon and George Wallace. The 1964 Republican nomination of Barry Goldwater produced quite a few defections. Primary challenges to Jimmy Carter in 1980 and George H.W. Bush in 1992 presaged high levels of inter-party voting in November.

There are also some exceptions; Republicans remained relatively united behind Gerald Ford in 1976 despite a primary challenge from Ronald Reagan. And there were high levels of Democratic unity behind Obama in 2008, although one can argue that a party having two good choices is a much lesser problem than it having none it can agree upon.

Overall, however, the degree of party unity during the primaries is one of the better historical predictors of the November outcome. That could be a problem for Republicans whether they nominate Trump or turn around and nominate Marco Rubio, Ted Cruz or John Kasich; significant numbers of GOP voters are likely to be angry either way.

It doesn’t necessarily mean that Republicans are bound to lose; I’d agree with David Plouffe’s assessment that a general election with Trump on the ballot is hard to predict and that Trump “could lose in a landslide or win narrowly.” But if I wouldn’t bet on an anti-Trump landslide, I’m also not sure I’d bet against one. The presumption that presidential elections are bound to be close is itself based on an uncomfortably small sample size: While three of the four elections since 2000 have been fairly close, most of them between 1952 and 1996 were not. Furthermore, the closeness of recent elections is partly a consequence of intense partisanship, which Trump’s nomination suggests may be fraying. The last partisan realignment, between about 1968 and 1980, produced both some highly competitive elections (1968, 1976) and some blowouts (1972, 1980).

Although what voters do will ultimately be more important, it will also be worth watching how Republican Party elites behave and how much they unite behind Trump. On Twitter this weekend, there was a lot of activity behind the hashtag #NeverTrump, with various conservative intellectuals and operatives pledging that they’d refuse to support Trump in November. Rubio’s Twitter account employed the hashtag also, although Rubio himself has been ambiguous about whether he’d back Trump.

It’s reasonably safe to say that some of the people in the #NeverTrump movement will, in fact, wind up supporting Trump. Clinton, very likely the Democratic nominee, is a divisive figure, and some anti-Trump conservatives will conclude that Trump is the lesser of two evils. Others will get caught up in the esprit de corps of the election. Some of them might be reassured by how Trump conducts himself during the general election campaign or whom he picks as his running mate.

But I’d be equally surprised if there were total capitulation to Trump. Instead, I’d expect quite a bit of resistance from Republican elites. One thing this election has probably taught us is that there are fewer movement conservatives than those within the conservative movement might want to admit. Rank-and-file Republican voters aren’t necessarily all that ideological, and they might buy into some of the Republican platform while rejecting other parts of it. They might care more about Trump’s personality than his policy views.

But there are certainly some movement conservatives, and they have outsized influence on social media, talk radio, television and in other arenas of political discourse. And if you are a movement conservative, Trump is arguably a pretty terrible choice, taking your conservative party and remaking it in his unpredictable medley of nationalism, populism and big-government Trumpism.

If you’re one of these ideological conservatives, it may even be in your best interest for Trump to lose in November. If Trump loses, especially by a wide margin, his brand of politics will probably be discredited, or his nomination might look like a strange, one-off “black swan” that you’ll be better equipped to prevent the next time around. You’ll have an opportunity to get your party back in 2020, and your nominee might stand a pretty decent chance against Clinton, who could be elected despite being quite unpopular because Trump is even less popular and who would be aiming for the Democratic Party’s fourth straight term in office.

But if Trump wins in November, you might as well relocate the Republican National Committee’s headquarters to Trump Tower. The realignment of the Republican Party will be underway, and you’ll have been left out of it.

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