BOSTON (AP) - Heading into the final weekend of the 2004 presidential campaign, John Kerry was feeling good about his chances of winning the White House.
The Democratic nominee thought he had bested President Bush in their three prime-time debates. He also felt he'd convinced Americans his military and foreign affairs experience left him better equipped to end the Iraqi war.
Then Osama bin Laden weighed in with the most recent "October surprise" to land with a thud on a presidential campaign.
Kerry believes bin Laden cost him the presidency by issuing a videotape that criticized Bush and warned U.S. voters that "your security is in your own hands" in the election. And the Massachusetts senator thinks that's instructive for both Democrat Barack Obama and Republican John McCain during the final month of their campaign.
From Henry Kissinger's declaration that "peace is at hand" in Vietnam a month before the 1972 election, to a report just before the 2000 vote that George W. Bush had once been arrested for drunken driving, last-minute sensations have demonstrated the potential to reshape a race.
"It changed the entire dynamic of the last five days," Kerry said this week of the bin Laden tape. "We saw it in the polling. There was no other intervening event. We saw the polls freeze and then we saw them drop a point, because all the security moms, it agitated people over 9/11."
Kerry added, "Whenever you're close to an election, things have more impact, you don't have time to respond, you don't have time to change the dynamics backwards."
That certainly was the concern in 1980, the election year that spawned the term "October surprise." In a twist of fate, the name grew out of a fear that never was realized.
Republican Ronald Reagan was challenging Democratic incumbent Jimmy Carter in 1980. Precisely a year before Election Day, a group of Islamic radicals had stormed the U.S. Embassy in Tehran, Iran, and seized American hostages.
President Carter worked throughout the campaign to secure their release, including launching an ill-fated rescue mission in April 1980 that killed eight U.S. servicemen. Critics say the Reagan team was so concerned that Carter would gain a boost by winning their release just before the election, that his campaign manager and others negotiated privately with the Iranians to ensure that did not happen.
It didn't, and Reagan ended up beating Carter. The 52 hostages were released Jan. 20, 1981 - the day the former California governor was inaugurated as president.
At least three books on the subject have the term "October surprise" in their title, although no conspiracy was ever proven.
Even though the month has just begun, the specter of an October surprise has already factored into the 2008 campaign.
Obama's campaign had to bat down reports that his former pastor, the Rev. Jeremiah Wright, was going to release a book this month. Obama distanced himself from Wright earlier this year after the preacher, among other things, suggested the U.S. government was capable of planting AIDS in the black community.
McCain's running mate, Alaska Gov. Sarah Palin, stopped cooperating with lawmakers investigating her firing of the state's public safety commissioner after one joked that the findings could amount to an "October surprise" for the vice presidential nominee. Sen. Hollis French, a Democrat, later apologized for the remark. Palin was to debate her Democratic rival, Sen. Joe Biden, on Thursday.
U.S. intelligence sources, meanwhile, have warned about the potential for another attack by bin Laden and al-Qaida terrorists, seen by some as a potential boost for McCain. The Arizona senator and Vietnam veteran has argued he has stronger national security credentials than his Democratic rival, a freshman senator from Illinois.
The same concern was voiced last spring by Harold Ickes, then an adviser to Obama rival Hillary Rodham Clinton.
In emphasizing the credentials of the New York senator and former first lady, Ickes said: "We don't know enough about Senator Obama yet. We don't need an October surprise. And (the chance of) an October surprise with Hillary is remote."
From Obama's perspective, an October surprise may have begun a month early: The turmoil in U.S. financial markets that erupted in September triggered criticism of McCain's leadership and economic understanding, and polls showed Obama starting to open a lead in key battleground states.
That movement could be reversed in the two remaining presidential debates - or by a true October surprise.
Kerry said any surprise deliberately engineered by one of the campaigns would be a risky endeavor.