WEST DES MOINES, Iowa — Mitt Romney appeared at a rally for Republican Senate candidate Joni Ernst Sunday night. Amid all the speculation that Romney might run for president yet again in 2016, he gave one small indication that he won’t: He told a joke. “Now when you run for office, people tell you you shouldn’t tell jokes,” Romney told the crowd. “But I’m not running for office, so I can tell one.” The joke was about President Obama: