Let's examine factors that might be favorable for Dems in 2020

"I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience.” 

Ronald Reagan’s 1984 quip, one of the most impactful presidential debate lines of the past 50 years, subtly and searingly turned a political weakness — concerns about his relatively advanced age  — into an asset. Never before had a 70+ year-old been a major-party presidential nominee. Since then, 11 more septuagenarians have run, with three winning their party’s nomination.

As more Democrats jump into the 2020 fray, it’s worth examining factors that might present electoral advantages in a crowded field. For example, there is a slight correlation between height and presidential electability. And aside from war hero Dwight Eisenhower, Americans haven’t elected a bald president in nearly 200 years

But what about age? Eight of our 58 presidential elections are difficult to parse, such as those where only one major-party candidate competed (1788, 1792 and 1820), or where multiple candidates across the chronological spectrum faced off. Among the other 50 races, the older candidate prevailed 28 times (56 percent).

However, much of this advantage stems from incumbency  — relatively old presidents running for re-election. Sitting presidents have run for second terms 31 times, winning on 21 occasions (68 percent). During open elections where everyone is a challenger, youth has prevailed 12 of 22 times (55 percent).

There are surprisingly clear age differences among the two major parties’ presidential nominees. Since the end of the Civil War, Democratic nominees have averaged 53 years old, four years younger than their Republican opponents. And this gap has widened ever since the presidential nominating process shifted dramatically beginning in 1972. During that election cycle, the Democratic National Committee instituted new rules that transferred some power away from party bosses and into the hands of rank-and-file voters through a more democratic and universal primary system.

Since those reforms were enacted, Democratic nominees have averaged 54 years of age, with only one (Hillary ClintonHillary Diane Rodham ClintonTrump rips Krugman, NYT after columnist writes GOP no longer believes in American values Klobuchar jokes to Cuomo: 'I feel you creeping over my shoulder' but 'not in a Trumpian manner' Dems seek to rein in calls for impeachment MORE in 2016) older than 60. During this same timeframe, Republican nominees have averaged 65 years of age. In 11 of the last 12 elections, the Republican was older than the Democratic opponent.

Digging a little deeper, since 1972, the average age of Democrats running for president has been 55. Twenty-five percent have been under 50 years old, while 26 percent have been over 60. 

But this seeming parity among “young” and “old” is misleading. In the six elections from 1972 to 1992, 21 Democratic presidential candidates (35 percent) were under 50, while 11 (18 percent) were over 60. But in the six elections since then, the Democratic fields have been markedly less youthful; only one candidate has been under 50 (Barack ObamaBarack Hussein ObamaTrump's regulatory rollback boosts odds of a financial crisis Five town hall takeaways: Warren shines, Sanders gives ammo to critics Ex-Obama CIA official makes 'Game of Thrones' cameo MORE in 2008) compared to 12 over 60.

It should be noted that a Democrat over 60 has been elected president only twice since the Civil War: Franklin Roosevelt in 1944 and Harry Truman four years later.

Meanwhile, since 1972, the average age of Republicans running for president has been 59 — four years older than their Democratic counterparts. Only 14 percent have been under 50, while 49 percent (nearly double that of Democrats) have been over 60. In fact, nine of their last 11 nominees (everyone except George W. Bush) have been 62 or older.

Finally, 18 times a president has run for re-election as the oldest of that year’s major-party nominees, prevailing 14 of those times (78 percent). Donald TrumpDonald John TrumpRussia's election interference is a problem for the GOP Pence to pitch trade deal during trip to Michigan: report Iran oil minister: US made 'bad mistake' in ending sanctions waivers MORE is older than each of the Democratic Party’s current crop of declared candidates. Of course, if age really does offer an advantage, Joe BidenJoseph (Joe) Robinette BidenAndrew Cuomo: Biden has best chance at 'main goal' of beating Trump Poll: Buttigieg tops Harris, O'Rourke as momentum builds Buttigieg responds to accusation of pushing a 'hate hoax' about Pence MORE, Bernie SandersBernard (Bernie) SandersAndrew Cuomo: Biden has best chance at 'main goal' of beating Trump Poll: Buttigieg tops Harris, O'Rourke as momentum builds Buttigieg responds to accusation of pushing a 'hate hoax' about Pence MORE, and Michael Bloomberg would have yet one more reason to take the plunge.

So what happened to Walter Mondale? Down 8-12 points for much of 1984, any chance of closing the gap went out the window at that October debate. He met Reagan’s sleight-of-hand “youth and inexperience” response with prolonged laughter. He was in on the joke, thereby inadvertently and tacitly lending credence to Reagan’s claim.

Mondale was 56 at the time — slightly above the average age of previous nominees. But in politics, how old you are might matter less than how old you seem. 

B.J. Rudell is associate director of POLIS: Duke University’s Center for Political Leadership, Innovation and Service. His nearly 25-year career has included stints on Capitol Hill, on a presidential campaign, in a newsroom, in classrooms and for a consulting firm. He has authored three books and has shared political insights on CNN, Fox News and dozens of radio stations across the country.