It’s been a perennial of presidential politics for almost half a century: the “October surprise,” a damning revelation about a candidate leaked just weeks before Election Day. Today’s news that the FBI investigation into Hillary Clinton’s private email server was being reviewed in the light of “new evidence” had headline writers using the term once again. And the revelation certainly fits the bill: Here we are just a week and a half before the election, and the potential for damaging news could upend Clinton’s lead in the polls.

Already, rival Donald Trump is taking full advantage of the revelation, telling a cheering crowd in New Hampshire today that Clinton is corrupt. And after weeks of claiming that the system is rigged against him, he expressed new hope that things would turn his way.

“It might be not be as rigged as I thought,” Trump told the crowd. “I think they’re going to right the ship, folks. I think they’re going to right this yet.”

But if history is any guide, Trump may not benefit from the news as much as he hopes.

Though long-ago presidential elections were upended by last-minute revelations, the term “October surprise” only really came into popular use after the 1972 contest between GOP incumbent Richard Nixon and Democrat George McGovern, which was shadowed by the unpopular Vietnam War. Just 12 days before the election, Nixon’s national security advisor, Henry Kissinger, announced that “peace is at hand,” which some say gave Nixon a boost and helped him win a landslide victory that year.

In almost every election since then, there have been “October surprises.” Most prominently, there were allegations that GOP nominee Ronald Reagan had cut a deal with the Iranian government in 1980 to delay the release of American hostages until after his campaign against incumbent Jimmy Carter. More recently, revelations emerged shortly before the contested 2000 election with Al Gore that then-candidate George W. Bush had once been arrested for drunk driving.

Yet according to some scholars, the October surprise doesn’t always have much of an impact on the election. For example, Bush’s drunk driving arrest made huge headlines and raised concerns about the candidate’s prudence, but it barely moved the needle in the polls, noted Peter Hamby in a Shorenstein Center study: “While 83 percent of the public said they had heard of the story—a huge percentage—only 17 percent said they actually found the story ‘informative.'” And, as we all know, Bush went on to squeeze past Gore and win the election.