The already large field of Democratic presidential candidates has grown again: Joe Sestak, a former Pennsylvania congressman with an extensive military background, said Sunday that he plans to seek the presidency. “I’m Joe Sestak, and I wore the cloth of the nation for over 31 years in peace and war, from the Vietnam and Cold War eras to Afghanistan and Iraq and the emergence of China,” he said in a video announcing his candidacy. A retired three-star admiral, Sestak represented Pennsylvania’s 7th congressional district for two terms, from 2007 to 2011, and has mounted two unsuccessful runs for the US...