In the span of a single news cycle, Republicans got a jarring reminder of two forces that could prevent them from retaking the presidency in next year. At sunrise in the East on Wednesday, Sarah Palin demonstrated that she has little interest — or capacity — in moving beyond her brand of grievance-based politics. And at sundown in the West, Barack Obama reminded even his critics of his ability to rally disparate Americans around a message of reconciliation. Palin was defiant, making the case in a taped speech she posted online why the nation’s heated political debate should continue unabated...