One evening last July, Senator John McCain of Arizona arrived at the New Hampshire home of Erin Flanagan for sandwiches, chocolate-chip cookies and heartfelt talk about Iraq. They had met at a presidential debate, when she asked the candidates what they would do to bring home American soldiers — soldiers like her brother, who had been killed in action a few months earlier. Mr. McCain did not bring cameras or a retinue. Instead, he brought his youngest son, James McCain, 19, then a private first class in the Marine Corps about to leave for Iraq. Father and son sat down...