It might be time to retire one of the most enduring cliches in modern politics: When it comes to choosing their presidential nominees, Democrats fall in love while Republicans fall in line.

Democrats in the last half century have frequently selected fresh faces for president: George McGovern over party elders like Edmund Muskie, the little-known Jimmy Carter, a freshman senator named Barack Obama. Meanwhile, Republicans time and again rewarded the runner-up from the last round of competitive primaries — Ronald Reagan, George H.W. Bush, Bob Dole, John McCain, and Mitt Romney. In the cases of Dole and McCain in particular, it felt as if Republicans were handing out their presidential nomination like a gold watch at a retirement party. A general election match-up between Donald Trump and Joe Biden would seem to throw these old patterns out the window.

Occasionally, Republicans have flirted with riskier general election candidates. Herman Cain and Michele Bachmann both led in national polls during the 2012 cycle. McCain's path to the 2008 nomination was especially complicated, as he faced a revolving door of competitors ranging from Fred Thompson to Mike Huckabee while also wresting the establishment mantle away from Rudy Giuliani. Dole lost New Hampshire to Pat Buchanan in 1996. But eventually the safe front-runner always prevailed, often helped by the fact that multiple challengers running to his right would split the vote.

Republican primary voters junked that model in spectacular fashion when they chose Trump in 2016. He is the overwhelming front-runner in the GOP primaries this time around too — no real viable alternative has emerged yet (sorry, Bill Weld). And Democrats seem poised to go with the safe choice for the second campaign in a row. Biden leads handsomely despite being older and involved in politics longer than Hillary Clinton, and he's also helped by multiple candidates splitting the progressive vote to his left.

Age has historically been no obstacle to winning the GOP presidential nomination. Reagan was just shy of his 70th birthday and Trump had already celebrated it. Republicans chose 68-year-old H.W. Bush to run against 46-year-old Bill Clinton, then 73-year-old Dole to take on Clinton at 50. McCain was 72 when he was the standard-bearer against 47-year-old Obama. Now 76-year-old Biden and soon-to-be 78-year-old Bernie Sanders are the top polling Democratic candidates, four years after the party nominated 69-year-old Hillary Clinton. It's still possible Democrats will pick a younger candidate for 2020. After all, there are nearly two dozen Democratic presidential contenders. But this is another way in which this year's Democrats look like Republicans in the past.

One possible distinction is that the Republican primary electorate consciously chose to break with their cautious past by nominating Trump and likely will do so again (though this time he is the incumbent). Democrats may have stumbled into their recent nominating habits simply because the dominant front-runners happened to be Hillary and Biden in successive cycles.

When Democrats have tried to follow their heads rather than their hearts, it hasn't always gone well for them. They flirted with Howard Dean before the 2004 primaries, as he claimed to represent the "Democratic wing of the Democratic Party." But they nominated John Kerry, who was safe and conventional, and paired him with John Edwards, giving them a ticket of two Democratic senators who had voted for the Iraq War. Shockingly, they did not beat Bush. And we all remember how 2016 ended up: with Clinton losing to a Republican who had a 60-percent unfavorable rating on election day.

Come to think of it, the Republicans' "fall in line" strategy hasn't always served them well either. Reagan and Bush 41 won three straight presidential elections with decisive Electoral College majorities. Bush 43 then went on to win two terms in his own right. Dole, McCain and Romney all disappointed.

Republican primary voters had long threatened their party's establishment by telling pollsters they'd consider various conservative firebrands, but did not act on those threats until Trump. Democrats spent the last presidential campaign playing it relatively safe. We'll see which strategy works this time.