How did this happen?

One possibility is that it’s mere randomness. It’s only one election that’s been roiled by Trump, you might think, and younger blood is waiting in the wings. But old age runs deep in modern presidential politics. Elizabeth Warren would also be the oldest president-elect in American history. The losers of the past two presidential elections, Mitt Romney and Hillary Clinton, were born months apart in 1947.

The mystery of America’s old presidential candidates is really two separate questions—one of demand, and one of supply. First, are there reasons today’s voters might prefer older candidates to younger ones? And second, why is the pipeline of viable presidential candidates so advanced in years?

The most obvious reason America’s presidential candidates are so old might be that Americans are getting older. Voters over 65 routinely go to the polls more often than young voters do, and political-science research has found that voters typically prefer candidates “who are closest to themselves in age.” This sounds like a universal formula: Older countries produce older politicians.

But since the 1980s, almost every European country has gotten older, while the typical European Union leader has actually gotten younger. In the United Kingdom, although people over 55 outvote people under 30 by one of the widest margins in the world, the current prime minister, Boris Johnson, is “only” 55. Biden, Sanders, and Trump are all older right now than the U.K.’s five previous prime ministers, going back to Tony Blair.

So the preference for very old candidates seems to be weirdly, specifically American. What’s that about?

Maybe it’s about decades of youth disengagement from politics. According to The Economist, older Americans have outvoted younger Americans by a wider margin than in the typical OECD country. This is particularly true at the local level. As Timothy Noah writes in Politico, studies have found that the median voter age in America’s municipal elections is 57—“nearly a generation older than the median age of eligible voters.”

Or maybe it’s about the American electorate’s preference for “experienced novices.” Since 1996, every new president has had less national political experience than the previous commander in chief had when he was elected. Bill Clinton was a fresher face than George H. W. Bush, but had more gubernatorial experience than George W. Bush, who in turn was a governor for longer than Barack Obama was a senator. And then came Trump, who had no political experience at all. If you extrapolate this trend, it might sound like America’s next breakthrough presidential candidate will be some 35-year-old YouTube influencer who just recently learned about the filibuster.

But audiences tend to gravitate toward extreme novelty when it’s paired with deep familiarity. Most people want to feel mildly surprised and simultaneously comforted by their media, whether film, television, or music. The perfect “familiar surprise” in politics might be a character quite like Trump: a well-known celebrity who also represents a shock to the political system. If the future of American politics is experienced novices, the scale may be subtly tipped toward comforting paternal figures who aren’t steeped in the poison of contemporary politics, either because they’ve been out of the game (like Biden) or because they’ve consistently rejected its rules (like Sanders).