Here's a frightening factoid for Donald Trump as he prepares totake office next month: Every Republican president since World WarII has been in power during at least one recession.

Of course, as the saying goes, past performance is notnecessarily indicative of future results. The billionaire developermay well avoid a downturn on his watch. But with the economicexpansion soon to become the third-longest on record, the risk of acontraction occurring during his time in office can't be cavalierlydismissed.

“Republican presidents seemingly can't do without” recessions,Joachim Fels, global economic adviser for Pacific InvestmentManagement Co., wrote in a blog post dated Dec. 12.

The same can't be said of Democrats. Outgoing President BarackObama did preside over an economic downturn in his first six monthsin office—one he inherited from his predecessor, Republican GeorgeW. Bush. John F. Kennedy took office just before a recession ended.And the U.S. entered and exited slumps when Jimmy Carter and HarryTruman were in charge.

But it was recession-free during the tenures of Democrats LyndonJohnson in the 1960s and Bill Clinton in the 1990s.

“The U.S. economy has performed better when the president of theUnited States is a Democrat rather than a Republican,” PrincetonUniversity professors Alan Blinder and Mark Watson wrote in apaper published in the American Economic Review this year.

The difference isn't due to more expansionary fiscal andmonetary policies under Democrats, according to Blinder, who servedin the Clinton White House, and Watson.

Instead it appears to stem from less costly oil shocks, a morefavorable international environment, productivity-boostingtechnological advances, and perhaps more optimistic consumers, theywrote. Some of those disparities may be down to better policies,but luck also played a role.

Fels cautioned against overestimating the ability of presidentsto prevent recessions—or to create them for that matter. After all,it's often the Federal Reserve that determines the ups and downs ofthe economy through changes in interest rates.

What's more, some Republican presidents just caught a bad break,Fels said. Dwight Eisenhower, for instance, took office in 1953when the U.S. was still enmeshed in the Korean War.

Others inherited recession-prone economies from their Democraticpredecessors. Inflation was running above 10 percent when RonaldReagan took over from Carter in January 1981, and then-Fed ChairmanPaul Volcker was determined to squelch it.

Trump said during the campaign that his plans would result in3.5 percent annual growth, well above the 2.1 percent pace of thecurrent expansion. Still, there's no denying the Republican recordwhen it comes to recessions. If Trump wants to ensure himself asuccessful presidency, that might be another party tradition theunconventional leader-in-waiting may have to break.

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