Listening to all this campaign mudslinging (just 12 more months to go!) I can’t figure out whether it’s the Republicans who are going to destroy the U.S. economy if they win the White House or if the Democrats will. I guess it depends on whatever side I’m watching, reading or listening to that day. This much is clear: each side is convinced that if the other side wins the White House, we’re going to hell in a hand basket.

But what does history tell us? How has the economy done under Democratic and Republican presidents? Has one side tended to be better for the economy than the other? As it happens, the answer—based on seven decades worth of economic stats going back to the end of World War II—is yes.

Since 1945, American voters have swung back and forth between both parties: seven Democratic presidents and nine Republican ones. Economic growth in real terms (in other words adjusted for inflation) averaged 2.54% per year under Republican presidents, but 4.35% per year under Democratic ones. That annual difference of 181 basis points, say Alan Blinder and Mark Watson, the two economics professors at Princeton who conducted the study, really adds up over time. It means that real GDP expanded 18.6% during a “typical Democratic four-year term, but only by 10.6% during a typical Republican term.” Adding more fuel to the argument, The Economist notes that better job creation and stock market performance also coincide more with Democratic presidents than Republican ones.

Here’s the part where you might say, yeah, but Congress is what counts here, because it controls the budget, taxes, passes economic legislation, and so forth. Fair enough. Yet over the same 70 year period—1945 to now—the government has been generally divided, with one party in the White House and one controlling at least one chamber of Congress (the House or Senate) 58 of 70 years. In just 13 years has one party controlled the White House and both chambers. In other words, government where power is divided among both ends of Pennsylvania Avenue has been not the exception, but the norm. So most presidents, whatever the party, have had to deal with the same thing: an opposition party that controlled part, if not all, of Congress.

So how to explain the better performance under Democratic presidents? Perhaps it’s just luck and timing. Or, perhaps, it’s philosophical differences. Take two of our more recent and economically successful presidents, Bill Clinton and Ronald Reagan. Reagan cut tax rates for the wealthy, but Bill Clinton raised them. Yet the Clinton economy slightly outperformed Reagan’s.

Perhaps federal deficits have something to do with it? Under Reagan, deficits soared; Clinton ran a surplus during his last four years in office. . But doesn’t federal spending, like Reagan’s, stimulate the economy? If so, then why didn’t Reagan’s spending increases and tax cuts produce faster growth than Clinton’s?

And then, this pattern was reversed by our two most recent presidents. Clinton’s tax increases on the wealthy were reversed by George W. Bush—and growth rates lagged. Under Barack Obama, the average federal rate paid by the top 1% of households went up, yet growth rates in the much-maligned Obama economy have outperformed the lower-tax rate Bush one. Go figure.

Even odder, Blinder and Watson point out that monetary policy—one domain of the Federal Reserve—has been “more pro-growth under Republican presidents.”

But don’t get too gleeful, Dems: One theory as to why things have been better under Democratic presidents has little to do with whoever’s president—and that is the many external factors that are largely beyond any politician’s control. For example, Clinton took office as the Cold War ended; he benefitted from the“peace dividend” that Reagan helped provide. Clinton also enjoyed the huge technology boom—the internet revolution—that boosted economic productivity throughout the 1990s. Just as Clinton left, the tech bubble burst—sparking a recession. And just as Bush inherited a downturn from his predecessor, he bequeathed one—far worse—to Obama. All presidents inherit, for better or worse, the economic conditions of their predecessor.

So what does all this mean for our next president? Whoever he, or more likely, she is will inherit a stronger economy than Obama inherited in 2009—but with plenty of time bombs. The deficit—down 70% on Obama’s watch, is back to its average post-war level relative to GDP. But it’s set to surge past $1 trillion again in the next decade, as unchecked—and mandatory—entitlement spending surges.

Assuming interest rates move higher in the years ahead, interest on the $18 trillion debt (up 80% since 2009) will rise, squeezing available capital that could go to more productive places. Then there are those lucky, external factors mentioned earlier. What happens if China continues to slow? The E.U. sinks into yet another recession? What if there’s, god forbid, another terror attack, or war breaks out and oil prices shoot back up? Who knows what could happen. The luck that has tended to help Democrats more than Republicans in recent decades could run out at any time.