Chinese immigration was a hot-button issue in the 1870s. In just a decade, more than 120,000 Chinese men and boys came to the United States under contract to work the railroads. Western states in particular were anxious about the influx of foreign labor and Democrats called for an immediate moratorium on Chinese immigration.

Republican candidate James Garfield took a more measured position, calling for new negotiations with China and for Congress to consider reasonable limitations on Chinese immigration that, “without violence or injustice, will place upon a sure foundation the peace of our communities and the freedom and dignity of labor.”

But just 12 days before the 1880 election, a letter emerged. Allegedly written by Garfield on House of Representatives stationary, the Republican candidate told a Massachusetts businessman named H.L. Morey that “individuals and companies have the right to buy labor where they can get it cheapest.” In other words, unrestricted Chinese immigration is good for business.

Democrats printed half a million copies of the “Morey letter” and distributed them in tightly contested states like California. They called it Garfield’s “death warrant.”

Republicans were slow to respond, but sent a team of private investigators to track down the letter’s recipient in Massachusetts. There was no H.L. Morey. Garfield declared the letter a forgery and published his handwriting side-by-side with the letter to prove it was a fake.

The forged letter did real damage, though, costing Garfield California. Although Garfield eventually won the election 214 electoral votes to 155, he barely won the popular vote by .02 percentage points.

Interestingly, the term “October surprise” was coined during an election where there wasn’t an actual October surprise.

In 1980, the Iranian Hostage Crisis cast a shadow over the presidential election. More than 50 American citizens were held hostage at the American Embassy in Tehran with no political solution in sight. Election Day would mark a full year of their captivity.

Ronald Reagan campaigned on a promise to free the hostages, something that President Jimmy Carter’s administration had failed to do. But inside the Reagan campaign, there was mounting suspicion that Carter had actually secured the hostages’ release, but was waiting to announce it during the final weeks of the campaign.

It was William Casey, Reagan’s campaign manager, who dubbed Carter’s alleged scheme an “October surprise.”

Time magazine reported, “[Reagan’s campaign] expects [Carter] to pull what they call ‘the October surprise,’ meaning that shortly before Election Day, he will inflate the importance of some overseas event in an attempt to rally the country around him.”

That didn’t happen, of course. Election Day came and went, the hostages remained in Tehran and Reagan won handily. The real surprise came on January 20, when Iran released the hostages just hours after Reagan's inauguration. Democrats then accused Reagan of striking a secret deal with Iran to hold the hostages until after he took office.

The Vietnam War was the major political issue of both the 1968 and 1972 elections. Even though the term “October surprise” hadn’t been coined yet, the idea was very much a political phenomenon. In both 1968 and 1972, incumbent presidents tried to secure last-minute peace deals to swing the election in their favor.

In 1968, President Lyndon Johnson chose not to run for reelection, but he was committed to helping his Democratic vice president, Hubert Humphrey, defeat the Republican candidate, Richard Nixon. On October 31, 1968, LBJ ordered a halt to all U.S. bombing campaigns in Vietnam, announcing “a major step toward a firm and an honorable peace in Southeast Asia.”

But just days later, the peace talks in Vietnam fell apart and Humphrey lost to Nixon. Democrats alleged that Nixon secretly scuttled the talks by promising the South Vietnamese stronger support if he were elected president. (Casey, who later coined “October surprise,” was a Nixon aide in 1968.)

Four years later, the Vietnam War was still raging and Nixon was adamant about securing peace before Election Day 1972. In early October, there appeared to be a breakthrough in the peace talks with the North Vietnamese accepting America’s terms for an end to the conflict. Behind the scenes, though, the South Vietnamese strongly objected to the arrangement.

That didn’t stop Henry Kissinger, Nixon’s national security advisor, from attending a press conference on October 26 and proclaiming that “peace is at hand.” In reality, the war would continue for another three years.

In 1992, President George H.W. Bush was fighting to hold onto the White House, but he faced some serious challenges. For starters, the U.S. economy was mired in a recession, never a good place for the incumbent. On top of that, the 1992 race saw the first serious third-party challenge in decades. Billionaire Ross Perot was running as a fiscal conservative and siphoning Republican voters away from Bush.

If Bush had hopes of defeating his Democratic challenger, Governor Bill Clinton of Arkansas, they took a serious hit in June 1992. That’s when Caspar Weinberger, who served as Secretary of Defense under President Reagan, was indicted for his involvement in the Iran-Contra Affair.

What’s the connection with Bush? Bush was Reagan’s vice president and had been trying to distance himself from the scandal, in which Reagan allegedly authorized illegal weapons sales to Iran in order to funnel money to the Contras, an anti-socialist army in Nicaragua.

Weinberger was the biggest name to be charged in the case, giving credence to the idea that everyone in the Reagan administration knew about the crime, including Bush. While Weinberger’s indictment didn’t happen in October, the timing was still bad for Bush, who lost the election to Clinton.

Greenberg says that the bad economy and the failure of Reaganomics were the biggest factor in Bush’s loss, but admits that “you never quite know what goes on in the mind of individual voters as they make their decisions close to Election Day.”

Bush pardoned Weinberger before he left office.

In the weeks leading up to the 2000 presidential election, polls showed that the race was a dead heat between George W. Bush and Vice President Al Gore. That’s exactly the type of election that could be decided by an “October surprise.”

Just days before Election Day‚ Fox News broke a bombshell story. In 1976, George W. Bush was arrested for drunk driving in Maine after a long night of partying. The revelation seemed to confirm unflattering portrayals of the younger Bush as unfit for office.

“I'm not proud of that,” Bush told the press in a statement. “I made some mistakes. I occasionally drank too much, and I did that night. I learned my lesson.”

The news story was a last-minute gift to Gore, who won the popular vote in 2000, but famously lost the election after a recount in Florida was halted by the Supreme Court.

Republican strategist Karl Rove argued that Bush’s “October surprise” cost him five states in the 2000 election, enough to have avoided the Florida recount altogether.

The 2016 election was chock-full of wild “October surprises.” On October 7, the Washington Post released a 2005 video of Republican candidate Donald Trump bragging about sexually assaulting women. That same day, Wikileaks released transcripts of Hillary Clinton’s speeches to Wall Street donors, which painted the Democratic candidate as pro-corporate. Then The New York Times reported that Trump hadn’t paid federal taxes in 18 years.

But all of those bombshell news items paled in comparison to what happened on October 28, just 11 days before the election. James Comey, the FBI director, called a press conference to announce that the intelligence agency was reopening its investigation into Clinton’s private email server—an investigation that the FBI had officially closed in July.

The resurrection of the email investigation—which had been the target of Republican ire for a year—delivered a crippling blow to the Clinton campaign. (In her memoir, Clinton said that Comey had “shivved” her.) Clinton lost the election by a narrow margin, despite winning the popular vote.

“There's been a lot of political science research about what they call ‘recency.’ That is to say, a big scandal in July probably is not going to matter that much, at least to most people, unless it completely derails a candidate," says Greenberg. "But the same scandal a week or two before the election, it sticks.”