These days, our political parties are defined by their presidents. Their policies and their programs tend to become their respective parties’ orthodoxies.

And the perceived success or failure of those policies and programs tends to determine how the parties’ candidates, even those who don’t support many of them, do at the polls.

This has been especially true in the past two decades, in which fewer Americans have been splitting their tickets or changing their minds from election to election than was the case from the 1950s to the 1980s.