The day after the Iowa caucuses, I watched as the Shakespearean drama underlying this year’s Republican race — a classic tale of friendship and betrayal — played out its final act on either edge of New Hampshire. In Keene, close to the Vermont border, I joined the small group of reporters who came to hear Jeb Bush speak to a polite audience of workers at a grocery wholesaler. Bush was, as ever, reasoned and respectful, but he seemed a little frustrated as he compared his old Florida protégé to President Obama. Marco Rubio is “gifted as a politician, an unbelievable...