Here's some advice to Democrats as they try to figure out which candidate to support for the 2020 presidential nomination: Don't worry too much about electability.

Yes, winning the election is the ultimate goal. But history shows that when parties pick their presidential candidates more with their heads than their hearts — when they pick a candidate they think is likely to win over the candidate they want to win — they usually end up losing.

So don't ask yourself which candidate is electable. Ask which candidate you want to elect, then act accordingly.

The best recent example of the electability trap came in 2004. Howard Dean, with his "I'm from the Democratic wing of the Democratic Party" shtick, appeared ready to be a significant force in the primaries, only to fall by the wayside when the media and voters abandoned him after the (much overplayed) scream heard 'round the world.

Dem voters eventually settled on John Kerry as their candidate — not because he inspired much passion, but because they thought he offered the best chance of taking the White House back from George W. Bush.

"Democrats say that what they are seeking above all this year is a candidate who can beat Bush," The New Yorker wrote that year, "and while Dean, campaigning as an antiwar, anti-establishment, outsider maverick, tapped the leaderless party's hot anger, the stolid war hero Kerry, with 20 years of experience in the foreign and domestic policy debates of the Senate, better fit the cold calculus of electability."

The New York Times' John Tierney saw the danger of that calculus: "Voters keep calling John Kerry the most electable candidate, the one most likely to defeat President Bush, and are quick to cite his many admirable and heroic qualities," Tierney wrote in February 2004. "But when they went to the polls in the Wisconsin primary last week, many seemed to have the same reservations about Mr. Kerry that Willy Loman had about his neighbor: He is liked, but not well liked."

Kerry ended up losing the general election to Bush. Not by a lot, but still, it says something that he wasn't even the most memorable speaker at his own convention that year. That distinction belonged to a newcomer on the national scene, an Illinois politician named Barack Obama.

Obama, whatever his faults, never had much of a problem generating passion among voters.

Why is electability a trap? Because it's all a matter of perception, and that perception is often shaped by risk-averse party elders and "conventional wisdom" media narratives more than voter preferences. So while it's not easy to define what makes a candidate electable, it's pretty easy to identify what makes them less so. In the Democratic Party, it's being unabashedly progressive. This has meant that candidates like Dean, Eugene McCarthy, pre-scandal John Edwards, and more recently, Bernie Sanders, have never quite gotten the benefit of the doubt from the Democratic establishment. That establishment support often makes a difference.

Republicans have their own version of this, with a tendency to nominate a candidate whose "turn" at the presidency has come. When they nominate candidates out of this kind of obligation — people like Bob Dole, John McCain, or Mitt Romney — the electorate's eyes tend to glaze over. When a candidate captures the passions of the base, like Ronald Reagan or Donald Trump, they tend to be more successful.

There's an obvious reason for this: Voting takes time and effort. Voters often want somebody who can get them excited, even passionate. That's more fun than voting out of mere obligation.

What does this mean for the 2020 primaries? The field hasn't settled enough to say. Sen. Kamala Harris (D-Calif.) jumped into the race over the weekend, and there are bound to be more following in her footsteps before debate season begins. That's OK. Let the candidates duke it out in the debates and primaries, and let's see if any of them earn the passion of voters.