Here’s what happened the last time a shocking election result caused chaos in markets (SPX, SPY)

President Harry S. Truman with a copy of the Chicago Daily Tribune that, based on early results, mistakenly announced “Dewey Defeats Truman.”Byron Rollins/AP

It has been a while since an election result was so shocking to investors that it triggered a big sell-off in markets.

The S&P 500 has been “loosely tracking” odds that Hillary Clinton will win next Tuesday’s election, according to Capital Economics’ Andrew Hunter.

But stocks fell, and polls tightened in Donald Trump’s favor, after news Friday of further FBI scrutiny into Clinton’s use of a private email server while she was secretary of state.

This raises the possibility of a period of deadlock after the election, Hunter wrote in a note on Wednesday. And that won’t be good for stocks.

An election result most recently caused real panic in the markets in 1948.

As Hunter recalled, Republican Thomas Dewey consistently led in the polls in the weeks before the election. And because he was Wall Street’s preferred candidate, stocks rallied.

But the incumbent, President Harry Truman, won the election, and Democrats took control of both the Senate and the House of Representatives. The race was so tight that the Chicago Tribune, then known as the Chicago Daily Tribune, mistakenly published that Dewey defeated Truman.

The S&P 500 fell by more than 10% over the next two weeks. Capital Economics

“An additional complication this year is Trump’s repeated claims that the election is ‘rigged’ and his refusal to confirm that he will accept the results if he loses,” Hunter said. “In the event of a very narrow Clinton win, it is all but guaranteed that Trump would aggressively dispute the election via the courts.”

Investors, like many other Americans, are impatiently waiting for the suspense of the election to be over so they can plan for the future with more certainty.

But there may not be a repeat of the 1948 slump — or even any drop at all — if there’s an election surprise next week. The lowest year-end forecast among strategists closely tracked by Bloomberg — 2,000, from Bank of America Merrill Lynch’s Savita Subramanian — implies a 5% drop from current levels.