How does this end?

Americans have long believed our country to be exceptional. That is true today in perhaps the worst possible sense: No other established Western democracy is at such risk of democratic collapse.

January 6, 2021, should have been a pivot point. The Capitol riot was the violent culmination of President Donald Trump and his Republican allies’ war on the legitimacy of American elections — but also a glimpse into the abyss that could have prompted the rest of the party to step away.

Yet the GOP’s fever didn’t break that day. Large...