John Kerry is in a tough spot. On the one hand, he wants his Vietnam experience to be his foremost national security credential. On the other, he doesn’t want anyone to focus on his activity in the immediate aftermath of his service. He really can’t have it both ways. So long as he makes the aspects of Vietnam he wants to emphasize a big issue, it’s perfectly legitimate for his critics to make those aspects he doesn’t want to focus on a big issue. For Kerry, Vietnam may turn out to be much closer to a wash than a big advantage, which could be devastating to his candidacy.