Opening a new battle with the White House, Senate Democrats on Wednesday abruptly blocked the approval of President Bush's nominee for a top public diplomacy job, charging that the administration had injected partisan politics into the drive to improve the United States' image overseas. The nominee, Dina Powell, the White House personnel director, had been expected to win broad approval to become deputy under secretary of state for public diplomacy, to be the second-in-command to Karen P. Hughes in charge of repairing the United States' reputation, especially in the Muslim world. But in what was to have been a routine...