This expansion has gone on for unusually long, by any number of measuring sticks. It has lasted twice as long as the average expansion since 1919. Just two postwar expansions have lasted longer, and not by much: There was the decade-long spell of growth that ended in 2001, and one eight-year stretch in the 1960s.

On top of that, Republicans have tended to see the economy tank shortly after coming into office. “Historically, every Republican president since Teddy Roosevelt has experienced a recession in their first term in office,” said Sam Stovall, the chief investment strategist at CFRA, an equity research group. “Every Republican president except one has had the recession take place in the first two years.” And nearly all modern-day presidents have faced one during their time in the Oval Office, including Barack Obama, George W. Bush, George H.W. Bush, Ronald Reagan, Jimmy Carter, and Gerald Ford. (Bill Clinton snuck out just in time.)

That said, there is no evidence that time itself kills economic growth. People seem to think of expansions as being like human bodies, developing problems as the years accumulate and thus naturally becoming more and more likely to perish. “Assorted imbalances and rigidities accumulate that hobble the economy and make it more fragile,” wrote Glenn Rudebusch, an economist at the Federal Reserve Bank of San Francisco, in an analysis published last year. “Thus, the recovery could be jeopardized by ever smaller shocks, and it becomes more likely over time that the economy will fall into recession.”

It turns out, he found, that this used to be true. Before World War II, the chance a year-old expansion would end in the next month was less than one in 20, and the chance a five-year-old expansion would end was nearly one in four. But the Great Depression spurred the federal government to enact policies to boost public spending when business and household spending declined, such as the unemployment insurance system. And the Federal Reserve learned how to stop banking panics and bolster lending when the economy slowed.

As a result, after the war, the chance a year-old expansion would end was still less than one in 20—as was that of a five-year-old expansion, roughly speaking. “Expansions, like Peter Pan, endure but never seem to grow old,” Rudebusch concluded.

Still, an economy close to full employment, which the United States seems to be, tends to grow for a shorter period of time than an economy far from it, Herzon said. “It’s not the age, but the maturity, that matters.” (As in so many things.) When the unemployment rate drops low enough to spur inflation—specifically, three-tenths of a percentage point or more below the non-accelerating inflation rate of unemployment, as determined by the Congressional Budget Office—the probability of a recession climbs.