When the calendar turns to October, thoughts turn to the joys of fall — pumpkins, hay rides Halloween.

For political junkies, however, October, particularly in an election year, means it’s time to speculate about the October surprise — that out-of-nowhere event that shakes up an election and forces campaigns and candidates to recalculate all of their assumptions.

Although it’s only Oct. 9, people have already cast two events as fitting the mold. The first was President Obama’s dismal debate performance last week, while the second, less than 48 hours later, was the release of the September jobs report showing unemployment dipping below 8 percent.

Maybe. Maybe not.

The relatively short history of October surprises suggests that 2012 has yet to produce a true October surprise.

It all began during the 1972 presidential campaign with President Richard M. Nixon. With the American public souring on the Vietnam War, his national security adviser, Henry Kissinger, proclaimed — out of the blue and with no obvious evidence — in late October that “peace is at hand” in Vietnam. Democrats cried foul, insisting that Kissinger’s pronouncement was all politics and no policy. Even Nixon conceded to chief of staff Bob Haldeman that he wouldn’t have said what Kissinger had.

Eight years later, the idea of an “October surprise” became cemented in the political culture, even though the surprise event in question never happened. Republicans were convinced that President Jimmy Carter was waiting until days before the election to announce the release of American hostages held in Iran. But, the election came without any release — and Carter lost. Iran agreed to release the hos­tages on the same day Ronald Reagan was inaugurated.

If the October surprise was born in the 1970s and early 1980s, it came into its own in 2000. That’s when — just five days before the election — it was revealed that the Republican nominee, Texas Gov. George W. Bush, had been arrested for driving while intoxicated in the mid-1970s. Bush’s mid-single-digits edge over Vice President Al Gore vanished, and Bush ended up losing the popular vote — although winning the presidency.

Four years later, a tape made by Osama bin Laden began circulating, a development that Democratic presidential nominee John F. Kerry told the Associated Press “changed the entire dynamic of the last five days . . . it agitated people over 9/11”.

The 2008 October surprise came in September, when the financial sector collapsed and the GOP nominee, Sen. John McCain, insisted that “the fundamentals of the economy are strong.” Whoops.

Maybe this election’s October surprise hasn’t arrived yet. There are 22 days left, after all.