It was just a firehouse chat with the guys of Engine 54 in lower Manhattan. But President Barack Obama delivered a message he hopes will also hit home with every American in this week of national catharsis: "You're always going to have a president and an administration who's got your back." In the denouement to the daring raid that brought down Osama bin Laden, the president has in effect been reintroduced to the nation. While taking care to strike the right tone — trying to savor the success of the dramatic covert operation without appearing to gloat — Obama has...