Bernie or Biden. Period.

If you’re a Democrat who doesn’t want Bernie Sanders to be the party’s nominee, your choice is now clear: You should vote for Joe Biden.

That’s the implication of Biden’s resounding victory in South Carolina. And Pete Buttigieg and Amy Klobuchar — to their credit — have both acknowledged this reality by dropping out of the race.

I realize it was only about a week ago that Biden’s campaign seemed grievously wounded, and he has still won only a single primary. So how has he so quickly become the only good alternative to Sanders?

There are four main reasons:

1) Biden holds a clear lead in the combined popular vote after the four first contests, with about 30 percent. Sanders has 24 percent, and Buttigieg has 16 percent. Next come Elizabeth Warren (10 percent) and Klobuchar (9 percent). Biden is first because he won South Carolina in a landslide, by an even larger margin than Sanders won Nevada, and because South Carolina is larger than either Iowa or New Hampshire. In the delegate count, Sanders holds a small lead over Biden, with no one else close.