The recognition—dawning rapidly on a gainsaying political establishment—that Donald Trump is poised not just to win more delegates on Super Tuesday than other GOP candidates, but to completely dominate this week’s 13 nominating contests, has confronted movement conservatives and loyal Republicans with a time for choosing.

The forces propelling Trump toward victory are driving party actors toward one of two determinations: Either Trump is the future of a Republican Party that current Republicans can live with, or the Republican Party is unsupportable with Trump atop its ticket. The latter would invite the kind of massive political realignment that only occurs in this country once or twice a century.

On Friday, former presidential candidate Chris Christie—the governor of New Jersey, and recently the chairman of the Republican Governors Association—made his choice clear by endorsing Trump. Moments later, Maine Governor Paul LePage followed suit. On Saturday, former Arizona governor Jan Brewer joined those two, and on Sunday, Senator Jeff Sessions of Alabama made it a foursome.

The counterweight to these conformists is embodied by #NeverTrump—a trending social media topic popularized by conservative activist Erick Erickson, and adopted most notably by Marco Rubio—which serves as a calling card for conservatives who are refusing to support Trump in a general election. The implication (which Rubio has refused to spell out directly) is that he will refuse to endorse Trump should he win the GOP nomination.

If this represents an enduring schism—if the ranks of resolute anti-Trump conservatives grows to include influential Republicans who had previously pledged to support the winner of the primary unconditionally—the significance will be hard to overstate. By closing in on the nomination, Trump is pitting conservatives’ commitments to party and movement against one another. If most Republicans were to fall into line behind Trump, the Republican Party apparatus would reorient dramatically, but it would survive. If instead the party’s leaders abandon Trump after promising otherwise, they would turn millions of people against the GOP enduringly. The damage to the Republican Party as an institution would be profound, perhaps fatal.