The discovery of multiple explosive devices addressed to prominent Democrats across the U.S. today has the potential to be the kind "October surprise" that could upend the midterm elections and perhaps even affect the balance of power in Congress.

William Casey, campaign manager for Ronald Reagan's 1980 presidential campaign, is said to have coined the term in the 1980s. But the concept of an 11th-hour revelation or event that could scramble everything in the month before Americans go to the polls predates the term.

Previous "October surprises" — not all of which have taken place in October — include:

2016 "Access Hollywood" Video

With then-candidate Donald Trump and Hillary Clinton battling it out for the presidency, the Washington Post published a bombshell story one month before the election that detailed a conversation Trump had with Billy Bush, then from “Access Hollywood,” in 2005 bragging about groping and kissing women without their consent. “Grab them by the p---y,” Trump said in the tape. “You can do anything.”

Release of the audio tape convinced Democrats they would win back the White House, but Trump went on to defeat Clinton in the presidential election by a convincing electoral-college margin despite losing the popular vote.

2012 Romney 47 Percent

As the 2012 presidential end, Mitt Romney, the Republican nominee, found himself in hot water after a secretly recorded tape of Romney was released from his appearance at a fundraiser.

“There are 47 percent of the people who will vote for the president no matter what,” Romney said in the recording. “All right, there are 47 percent who are with him, who are depending upon government, who believe that they are victims, who believe the government has responsibility to care for them.”

The tape played into the image of the former Massachusetts governor as an out-of-touch plutocrat and Romney later told Fox News that the video “did real damage to my campaign." President Barack Obama went on to win re-election.

2008 Market Crash

As Sen. John McCain, R-Ariz., went head-to-head with then-Sen. Barack Obama, D-Ill., in the 2008 election, the stock market suffered significant losses the month before Americans hit the polls. The crash came after Lehman Brothers filed for bankruptcy in September and as Americans began to feel the impacts of the Great Recession.

McCain had been edging ahead in some polls when the crash happened but ended up on the wrong end of a resounding loss.

2006 Rep. Mark Foley Scandal

In the run-up to the midterm elections in 2006, there was a bombshell revelation that Rep. Mark Foley, R-Fla., sent sexually explicit messages to male congressional pages. The scandal fed into the Democrat narrative that Republican rule had led to a "culture of corruption" in terms of both sex and money. Democrats ended up taking control of the House of Representatives for the first time in 12 years.

2004 Osama Bin Laden Video

On Oct. 29, 2004, Osama Bin Laden released a video tape discussing the upcoming presidential election. In the tape, bin Laden criticized then-President George W. Bush, causing a number of Republicans to claim that the al Qaeda leader had "endorsed" Democratic nominee Sen. John Kerry.

Kerry later told NBC’s “Meet the Press” that the tape caused him to drop in the polls and lifted Bush, who was re-elected.

2003 California Recall Election

Just before the October gubernatorial recall election in California, the Los Angeles Times reported that six women accused Arnold Schwarzenegger of sexual misconduct in incidents that occurred over three decades.

Three women alleged Schwarzenegger grabbed their breasts, the fourth said he grabbed her buttocks, the fifth women said he groped her in a hotel elevator and tried to take off her bathing suit, and the sixth alleged Schwarzenegger asked her sexually explicit questions.

Schwarzenegger’s campaign spokesman said at the time the former bodybuilder’s political opponents were deliberately trying to hurt his campaign. California voters nevertheless ended up electing Schwarzenegger as their governor.

2000 Bush Drunken Driving

Just before Election Day in November 2000, Fox News released a report that President George W. Bush had been arrested in September 1976, when he was 30 years old, for driving under the influence. Bush had pleaded guilty to a misdemeanor charge and paid a $150 fine.

Bush told reporters that the incident occurred on Labor Day weekend in Kennebunkport, Maine. He said he didn’t want to make the incident public to protect his twin daughters. Many Republicans were furious that he had not come clean earlier and to this day operatives on his campaign believe that the mistake led him to lose the popular vote and become embroiled in the controversial Florida recount.

1992 Iran-Contra Indictment

Just four days before George H.W. Bush, Bill Clinton, and Ross Perot faced off in the presidential election, Caspar Weinberger, former defense secretary for Ronald Reagan, was indicted on charges related to the Iran-Contra affair. Bush ended up losing the election and then pardoned Weinberger before he left office.

1980 Iran Hostages

Days before the presidential election which had Ronald Reagan challenging President Jimmy Carter, Iran announced it would not release American hostages until after the vote. Reports at the time alleged Reagan’s campaign secretly negotiated a deal with Iran to delay the release of the hostages until after the election, though officials with the Reagan campaign always disputed that.

Reagan won resoundingly, carrying 44 states. Iran freed the 52 Americans on the day of Reagan’s inauguration, giving him a major boost at the start of his first term.

1972 Nixon Peace Agreement

In later October, as President Richard Nixon was in the throes of the presidential campaign against Sen. George McGovern, D-S.D., Nixon’s national security adviser Henry Kissinger announced “peace is at hand” and said an agreement to end the Vietnam War was near. But Kissinger’s declaration came early, as negotiations broke down two months later. A peace accord was eventually signed in January 1973.

Nixon won 49 states, trouncing McGovern in a landslide equaled only by Reagan in 1984.