“The history is very clear on what happens when you challenge a sitting president like this,” the congressman told Bob Costa. Ronald Reagan’s challenge to Gerald Ford in 1976, Ted Kennedy’s to Jimmy Carter in 1980, and Pat Buchanan’s to George H. W. Bush in 1992 were all followed by a general-election victory by the other party.

The fear that a primary challenge to an incumbent president will doom the party that engages in it may be overblown — maybe serious challenges are a result of incumbent vulnerability more than a cause — but it probably explains why we haven’t seen a real one since 1992.