Updated

An "October surprise" is part of the political folklore of presidential campaigns, and just eight days before the election, the unexpected is indeed happening.

Monday's disclosure that 80-year-old Chief Justice William Rehnquist (search) has thyroid cancer immediately propelled the Supreme Court and the hot-button abortion issue onto the front burner, while the revelation about the looting of 377 tons of high explosives in Iraq gave John Kerry (search) an opening to accuse President Bush of "incredible incompetence."

Another troubling issue for Bush was the execution-style slaying of about 50 newly trained Iraqi soldiers, underscoring the chaos that still rages 19 months after the president ordered a U.S.-led invasion. As awful as the massacre was, it would have been much worse for Bush in political terms if the victims had been Americans.

In a tight race, Kerry and Bush are both on guard for outside events large and small that could not have been anticipated. Rehnquist's illness and discussions of his legacy recalled his pivotal vote four years ago in the decision that gave Bush the presidency after a disputed election outcome.

Traditionally, an October surprise is seen as a last-minute trick up the sleeve of the party in power to influence the election's outcome, such as Henry Kissinger (search) saying in 1972 that peace was at hand in Vietnam as his boss, Richard Nixon (search), sought re-election. In 1980, Ronald Reagan's campaign worried that President Carter would somehow engineer a last-minute release of American hostages in Iran — but they were not freed until the day Reagan was inaugurated and Carter left Washington.

This year, Democrats have speculated that the White House might spring the capture of Osama bin Laden or another terrorist leader to try to seal Bush's re-election.

But as Monday's news demonstrated, surprise developments can emerge outside of anyone's control and can just as easily work against the incumbent — particularly a development like the grisly, roadside murder of Iraqi soldiers.

"There's no way in which Bush can say, `Look, it was only 50 people, they were only Iraqis,'" said Princeton political scientist Fred Greenstein. "It makes it very hard for him to use his mantra about things are getting better and better, and this is right down to the countdown."

Kerry seized on the news about hundreds of tons of missing explosives in Iraq to try to undercut Bush's claim that he is best qualified to protect Americans and lead the war against terror. International Atomic Energy Agency chief Mohamed ElBaradei (search) blamed the loss on a "lack of security."

Kerry said Bush had "miscalculated about how to go to war, miscalculated about the numbers of troops that we would need, miscalculated about sending young Americans to war without the armor they needed, without the Humvees they needed that were armored."

Bush shot back, "My opponent has the wrong strategy for the wrong country at the wrong time."

In the highly charged political atmosphere of the final days, Kerry's camp suggested the administration had leaked news of Rehnquist's hospitalization to divert attention away from the missing-weapons story. White House officials laughed off the idea.

Rehnquist's hospitalization reminded voters that the next president, in all likelihood, will have the opportunity to name one or more Supreme Court justices who will deal with divisive social issues such as abortion, affirmative action, gay rights and religion. Eight of the nine are 65 or older.

There also was the suggestion of a leak of stories about the missing explosives. ElBaradei said the IAEA had been trying to give the U.S.-led multinational force and Iraq's interim government "an opportunity to attempt to recover the explosives before this matter was put into the public domain." But he decided to report the loss to the Security Council once it was reported in the media.

White House communications director Dan Bartlett said the missing weapons story was no last-minute surprise, having been reported earlier this month — although without the graphic details of the new report. Moreover, he said, "The American people are well informed about the issue about Iraq and the fierce battles that are taking place there." He said the deaths of the Iraqi recruits were "dramatic" and "catastrophic" but would have a much greater impact if they had been Americans.

Greenstein said Iraq hangs over the campaign's countdown. "The situation is so loose and fluid and explosive. Who knows what will detonate into the picture totally out of the blue."