Well, for Republicans, it eventually didn’t matter in 2016. The arguments against Donald Trump all started with the premise that he was unelectable in a nationwide campaign. The conventional wisdom said that Trump had his base, but the base wasn’t enough to win in enough places around the country to make a dent.

Democrats are now wading through a primary, that seems to grow with new candidates almost weekly, and the decision they’re making is one based on finding a candidate who, by most accounts, is both “electable” yet able to unite all factions of the party.

Bernie Sanders is popular among the base, but is Bernie “electable” to most Americans? Some would say absolutely not, but then the same people might have said that about Donald Trump, so maybe we should toss out conventional wisdom for now.

Joe Biden seems to be so “electable” that he’s practically skipping the primary and moving on to the general election. He’s electable in the eyes of conventional wisdom, but is he electable in the eyes of Democratic primary voters? So far, the polls tend to agree, though he has ardent detractors among progressives in the party.

For example, some new video resurfaced of Biden praising former vice president Dick Cheney in 2015, calling him a “decent man” who Biden is fond of. This sort of baggage does not sit well with progressive activists:

Does it matter, though, if Biden is not palatable to a small, yet vocal, part of the Democratic Party base? Donald Trump wasn’t palatable to a sizable number of Republican establishment figures, many of whom still hold the same disdain for the man occupying the White House to this day as they did during the 2016 primary.

I suppose the difference lies in the fact that the Republican Party base adored Trump in the primary, while Biden may have the opposite problem. He is loved by many in the party and remains their default choice, but he’s got some baggage that makes him “unelectable” in the eyes of some progressive Democrats.

In a piece out on Thursday in the Washington Post, author Philip Bump explores the question of how voters decide which candidate is “electable” and which candidate is not by examining how Democrats selected a candidate in 2004, another year when they were running against an incumbent Republican president:

In October 2003, as Democrats were jockeying for the opportunity to face George W. Bush in the 2004 presidential election, The Post and our polling partners at ABC News surveyed Democratic voters to gauge their preferences for a nominee. At the time, former Vermont governor Howard Dean had a slight lead. The candidate who the most respondents saw as most electable, though, was Sen. Joe Lieberman of Connecticut.

Well, given the margins of error, Lieberman, Dean and two other candidates were all sort of mushed together as most supported and most electable. That’s one key pattern here: The candidates that are seen as most electable are generally also those who have the most support.

So the eventual nominee, Sen. John F. Kerry of Massachusetts, was in fifth on both metrics. Not much support, not generally seen as electable.

Of course, Kerry lost. Perhaps Lieberman, who’d nearly been elected vice president four years prior, really would have been more electable. That’s another problem with these assessments of electability: It’s nearly impossible to determine how accurate the predictions were since there are no countervailing scenarios in which other candidates ended up facing off in the general election.

In 2003, Lieberman would have been unpalatable to progressive activists given his moderate credentials. Howard Dean would have been a better choice for them, but he went down in a screaming rage after losing the Iowa caucus. Kerry was a good compromise for the party, but he lacked any sort of excitement or draw needed to upset an incumbent president.

Bump also examined the Republican field in 2008:

In October 2008, the candidate viewed as most electable wasn’t the eventual nominee, Sen. John McCain of Arizona — it was former New York mayor Rudolph W. Giuliani. From October to December, Giuliani lost support for his candidacy as former Massachusetts governor Mitt Romney, now a U.S. senator from Utah, surged. McCain, too, lost both support and a sense that he was most electable. The two move in tandem: A candidate that gains support is also seen as more electable.

Electability, as Bump explains, is a self-fulfilling prophecy. If a candidate gains polling support, suddenly more voters see them as “electable” despite the fickle and often inaccurate nature of public opinion polling.

Then there was Texas Gov. Rick Perry in 2012, who on paper seemed to be the most “electable” for Republicans until his major debate gaffe:

A really, really great example of that came in 2012. The Post and ABC polled in September and October of that year, witnessing a massive shift in how Republicans viewed the field. In the October poll, Texas Gov. Rick Perry had a lead and was seen as the most electable.

During a debate in early November, though, Perry suddenly forgot one of the three federal agencies he wanted to shut down. His “oops” response came to define his candidacy, and it collapsed. Businessman Herman Cain and Romney picked up much of the slack.

One gaffe, one incident, can torpedo a candidate’s chances, making electability a tricky thing to evaluate in the abstract.

The lesson to take from all this has to do with understanding that each candidate is just one bad performance away from becoming “unelectable.” Or, are they? Donald Trump never seemed to become “unelectable,” he started out that way and won regardless.

Joe Biden seems very electable, and it’s hard to imagine a scenario where he truly gaffes to the point of changing minds in that matter. He’s a seasoned politician who has spent years in the national spotlight. Does he say dumb things sometimes? Yes, yes he does. The public, however, seems to bake that in and forgive him because, well, he’s “Uncle Joe,” and that’s just the way he is.

Progressive activists in the Democratic primary are not going to like Joe Biden, but they would like defeating Donald Trump. If Biden becomes the nominee, they’ll need to reconcile those views.

If you want to defeat Trump, however, the floundering campaign of Beto O’Rourke may give you a better argument for electability according to a CNN poll (PDF) released this week:

CNN Democratic poll 2020

Beto, in theory, would beat Trump on the national stage by 52 percent to 42 percent. Biden would only accomplish this beating Trump at 51 percent to 45 percent. The only Democrat underwater against Trump, in this poll, is Elizabeth Warren.

These are national numbers, however, and just ask Hillary Clinton how important national polling leads are when it comes to winning the Electoral College. Still, these numbers give you an idea of the national sentiment when it comes to judging the ever-expanding Democratic field.

If electability matters, then choose wisely, because electability can change quickly as Howard Dean, Rudy Giuliani, and Rick Perry all discovered.