DONALD J. TRUMP has made a shrewd bet. For the first time since he descended an escalator in Trump Tower last June to announce that this time, he really was running for president, he ceded control of his campaign message. He handed the Trump-bedecked podium over to Sarah Palin. Mr. Trump’s bet: When the politician most fluent in American rage roars, the movement she gave voice to in the fall of 2008 will roar back today.