Republicans have an unusual political problem in Alabama: Their candidate may win.

We’re talking about Roy Moore, who is neck-and-neck in the polls against Democratic candidate and former U.S. Attorney Doug Jones for the Senate seat vacated by Jeff Sessions. By now there cannot be a soul in America unaware of allegations that, as a 30-something assistant district attorney, Mr. Moore had inappropriate sexual contact with underage girls, including one as young as 14.

The...