“The Tonight Show” host humanized a dangerous man on Thursday night. Jimmy Fallon had Donald Trump on “The Tonight Show” Thursday night, and all some people could talk about afterward was a head rub. Toward the end of the interview, Fallon asked the Republican presidential nominee if he could mess up his famous head of hair on live TV, leading to raucous applause and the sort of bite-sized video that both the creators and consumers of internet media eat up. Before the rub, Fallon did sneak in a few subtle quips, like asking Trump if he knew what a coin...