While many believe it’s a foregone conclusion that Hillary Clinton will win the 2016 presidential election, top strategist Kenneth Fisher says history shows otherwise –and that, he says, is likely to have a big impact on how stocks behave over the next couple years.

“An old, little-known truth: Overwhelmingly, when Republicans are elected President, stocks soar during the year they are elected (this has held true every single election since World War II, except 2000, an election in which Al Gore won the popular vote),” Fisher writes in his latest Forbes column. “Average S&P 500 gain: 12%, presumably in anticipation of market-friendly policies. Then stocks flipped negative during most GOP inaugural years–presumably when investors realized the new guy was, yes, still just a politician.”

Fisher says the opposite is true in years when a Democrat is elected –anticipating antibusiness policies, the market usually lags. But in Democrats’ inaugural years, when investors have realized “the new guy was, yes, still just a politician”  and things wouldn’t be so bad, Fisher says, stocks on average have surged more than 20%.

So why does Fisher think Clinton won’t win in 2016? He says he’s discovered a trend of which few seem to be aware. “Since the Civil War we’ve elected Democrats who were either (1) already President or (2) a fresh new face (Obama, Clinton, Carter, Kennedy, FDR, Woodrow Wilson, etc.),” he writes. “Democrats have never elected anyone who would have been considered a likely nominee during the previous election cycle (Walter Mondale, Hubert Humphrey, Al Smith, etc.).”

Fisher offers one possible reason for this trend, which seems to be impacting his expectations for the next couple years. “I’m looking toward a great 2016 market–and increased 2017 risk,” he says.