Des Moines — Faced with a bounty of potential candidates vying for the Democratic presidential nomination, party voters appear to be putting a premium on electability, a signal of a more strategic approach to the selection process.

Interviews with voters and strategists show a baseline for support coming into focus for 2020: Can this candidate beat President Trump?

"I didn't know it was that bad to lose," said Des Moines resident Debbie Whittie, who came to check out one of Elizabeth Warren's events over the weekend. Whittie, who works for a credit union, says she is more engaged in political news than ever before. "I'm already worried about that," she said when asked about electability. "I really think I should go for 'the best,' but that consideration is going to have to be in my best."

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Jeanne Williamson, another Des Moines resident and a Democratic caucus-goer, said she will be taking a hard look at how the candidates stand on various policies. But, "That's my first reaction: to beat Trump," she said while standing in line to see Warren on a chilly Saturday evening.

"I would vote for anyone probably who could defeat Trump," said Sally Carney, another Iowa Democratic voter. "Oh, it's the most important: get him out," said Cathy Sanchez, a preschool teacher who came to Warren's event in Council Bluffs. Bill Shackelford, a retiree, said he wants "someone who is not subject to being characterized by the right wing" and therefore vulnerable to defeat by Mr. Trump. "Don't underestimate him," he said of the president.

"People are going to want to see how the person can match up to Trump," said Mike Vlacich, a New Hampshire Democratic strategist who managed Hillary Clinton's campaign in the state. "Voters are going to try to visualize this person on a debate stage with Trump and on social media and ask, does this person have what it takes?"

In that way, a voter is "going to be a little more of a political scientist," Vlacich said, and "less interested in sending messages or proving points, but making sure we have what it takes to win the White House back."

Who that candidate will be is anyone's guess at this point. And voters had varying views about how to beat Trump, whether it be through character and policy contrasts, inspiration and passion, or adopting the incumbent's own tactics. But the sentiment is driving interest and attendance at political events at this early stage in the cycle. And the prospect of taking Mr. Trump on is attracting what is expected to be the largest Democratic field in two decades.

"For the last generation, [when] there has been such an overwhelming presence of individuals on the Democratic side, a lot of Democrats didn't see a path to victory," said New Hampshire Democratic Party Chairman Ray Buckley. "Donald Trump has convinced every single person on every street corner in America that they could do a better job as president."

Massachusetts Sen. Elizabeth Warren, former Housing and Urban Development Secretary Julian Castro, and former Maryland Rep. John Delaney are the only candidates who have so far made official moves towards presidential bids. But several others are at least seriously considering bids, including a number of incumbent senators, former mayors, businessmen, and a former vice president.

Electability, though, is difficult to measure, particularly at this stage in the cycle. And perceived electability doesn't always equal success, as the 2016 election most recently demonstrated to Democrats. But the reaction among Democratic voters to the current president is so viscerally negative that it has become a unifying force in the party.

Some Democrats are concerned about the official party operation getting too involved in picking who is the most electable. And the Democratic National Committee is making an effort to be as inclusive as possible, as evidenced by their debate schedule and overall strategy. Activists, too, acknowledge the concern about letting the perfect be the enemy of the good.

"There's definitely a pragmatic streak. We're not going to throw the baby out with the bathwater," said Neil Sroka, spokesman for the progressive activist group Democracy for America. "No doubt defeating Donald Trump is the priority. But we have to be more than a party standing against Donald Trump. We have to stand for something."

In her stops through Iowa over the weekend, Warren did not mention Mr. Trump by name. Instead, she aimed to introduce herself to voters as a "fighter" for the middle class and for a "fairer" economic playing field. One voter asked why she gave Mr. Trump "fodder to be a bully" by releasing a DNA test, a signal that some may not like a candidate who plays the president's game. Others thought the approach showed a certain toughness, or didn't matter much to them at all.

Warren has shown a propensity for sparring with Mr. Trump, particularly through his preferred medium of Twitter. But in Iowa, she made a point not to make the trip about him. She did, however, try to pitch herself as having a broader appeal beyond her current fan base.

"We gotta stay focused on what matters to us. And what matters to us is that everybody gets a fighting chance," Warren said. "You don't have to persuade people ... Democrats, Republicans and independents get it."