Anyway, ticket-balancing is not the only successful approach, as Bill Clinton understood. When he clinched the Democratic nomination in 1992 as a Southern moderate, it was widely assumed he would pick a Northern liberal, as Jimmy Carter had.

Instead he chose a fellow Southern Baptist of his own generation with a reputation for moderation and congressional experience in national security issues, Al Gore. They were from adjoining Southern states and when the ticket was announced they met on the bridge between West Memphis, Arkansas, and Memphis, Tennessee.

This unbalanced ticket won two elections, carrying six of 14 Southern states in both 1992 and 1996. Democratic nominees from Massachusetts, both with Southern running mates, carried none in 1988 and 2004.

A similar approach for Mitt Romney would be what opponents might call a double-vanilla ticket, with another white male as vice presidential nominee.