Walter Shapiro: Trailing by a double-digit margin in the polls in the waning weeks of his 2006 Senate reelection campaign in Pennsylvania, Rick Santorum went nuclear. He did so not by launching vicious new attacks on his soon-to-be-victorious Democratic opponent, Bob Casey, but by indulging his own obsession with mushroom-cloud politics. He began speaking incessantly about the potential threat from a nuclear-armed Iran.
