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LOS ANGELES – With President Donald Trump's fate seemingly secure in the Senate's hands following his impeachment, the leading Democratic candidates to unseat him turned with fresh urgency Thursday night to the question of who is best positioned to beat him at the ballot box next fall.

Voters' concerns about "electability" seem to be intensifying as they get closer to casting ballots in the Democratic caucuses and primaries, which begin in Iowa on Feb. 3 and New Hampshire on Feb. 11.

A Gallup poll in November found that 60% of Democrats gave priority to a candidate who has the best chance of beating Trump rather than choosing one who agrees with them on issues, a sharp contrast with previous contests.

In Thursday's debate, an argument about what electability means ran through the debate. The candidates repeatedly emphasized disparate theories about what it will take to win in 2020: nominating an experienced politician or a Washington outsider, a strong progressive or a more moderate coalition-builder.

"Let's talk about how we win an election, which is something everybody here wants to do," said Sen. Bernie Sanders of Vermont, arguing that an inspirational progressive agenda was needed to drive turnout high enough to beat Trump.

Sen. Elizabeth Warren of Massachusetts, who largely shares that part of Sanders' theory of the race, argued that an anti-corruption fighter like her is needed to provide clear contrast to Trump.

On the opposite side were the three more centrist candidates — former Vice President Joe Biden, Sen. Amy Klobuchar of Minnesota and Mayor Pete Buttigieg of South Bend, Ind. Although the three differed from one another, especially in the case of Klobuchar and Buttigieg, they shared a view that defeating Trump requires an emphasis on pragmatism over ideology.

"We all have big progressive plans; the question is who can deliver on those plans," Biden said. "Who has the best chance, the most likely chance, of defeating Donald Trump?"

Polls show that at least a sizable plurality of Democratic voters perceive Biden as the safest bet to beat Trump.

Buttigieg repeatedly suggested — without mentioning Biden by name — that Washington experience had failed to address festering problems that gave rise to Trump's election.

"We've got to break out of the Washington mind-set that measures the bigness of an idea by how many trillions of dollars it adds to the budget or the boldness of an idea by how many fellow Americans it can antagonize," he said.

The candidate who made the bluntest argument about electability was Klobuchar.

"We should have someone heading up this ticket that has actually won and been able to show they can gather the support that you talk about with moderate Republicans and independents, as well as a fired-up Democratic base, and not just done it once," she said.

Klobuchar repeatedly emphasized her Midwestern background, insisting that her electoral success in Minnesota shows that she can win in other battleground states.

"It's not flyover country to me," she said. "I live there."

She added, "This primary comes down to some simple questions: Who has the best ideas, the best experience? And mostly, who can beat Donald Trump?"