Trump seems to get under the skin of some candidates, but not Rubio. And I have a theory as to why. It goes back to something I read about Lee Atwater, the infamous strategist who helped George H. W. Bush defeat Bob Dole in 1988. Atwater was a master at psychological warfare. As author John Brady reconuts in his book, Bad Boy The Life and Politics of Lee Atwater, he believed that “adults could be divided into two groups: the overly mature and the childlike.”

“The overly mature,” Brady writes, “are inflexible and overserious, making them highly vulnerable in politics, particularly in the age of television. [Bob] Dole was the mature type, Atwater the child.”

My theory is that Rubio still has enough of a “childlike” quality—I’m not talking about “childishness,” but a sort of “neoteny” whereby he has tempered his thoughtful conservative side with a playful or youthful, devil-may-care side—to make him actually enjoy Trump’s juvenile antics.

Back to Atwater, Brady writes: “It didn’t take Atwater much research to see that Dole was hypersensitive about attacks on his wife. Replaying old charges against her in Iowa, Atwater was able to get under the senators’ skin.”