The jokes popped up almost immediately that Mark Sanford was the luckiest guy on earth after word broke that Michael Jackson had suffered a heart attack. But the notion that Jackson's death, which preempted virtually all other news coverage on the cable networks last night, is sucking up media attention from other matters carries a dark edge to it as well. National-security experts are warning that without sustained attention on Iran, its repressive tactics could grow more deadly in the coming days.