Sen. John Kerry talks about his four months in Vietnam — it's a centerpiece of his presidential campaign — but there's one thing he won't talk about: the day he killed a Vietcong soldier at close range and earned a Silver Star. "It's a key part of him," said a Kerry friend. "It was a pivotal moment in his life. But he doesn't talk about it." Added another source close to Kerry, "it's the reason he gets so angry when his patriotism is challenged. It was a traumatic experience that's still with him, and he went through it for his...