Once Trump is nominated, America will have crossed a line.

A man who does not respect constitutional limits and who preys upon vulnerable minorities will lead one of the two major parties. The consequences, though hard to measure, could be profound. A few days ago in Iowa, fans at a high-school basketball game chanted, “Trump,” at the opposing team, which comprised Latino, African American, and Native American players. They wielded the name of the man who could become president as a racial slur. Protesters at Trump’s rallies have been beaten. Last year, in Boston, two men beat a Hispanic man with a metal pipe while yelling, “Trump was right.” Just imagine what might happen if were Trump nominated or, God forbid, elected. In myriad ways, America would become an uglier, scarier place.

If Rubio won, by contrast, the Republican Party might be stabilized. The terms of debate between the two parties would remain roughly the same. Given how radical even “establishment” Republicans like Rubio actually are, that’s a depressing prospect.

Nominating Trump would upend all that. American politics would fundamentally change. But as conservatives have often reminded liberals, change does not equal progress. Sometimes even a morally corrupt status quo is better than what follows. A Trump nomination would represent a leap into a terrifying political unknown.