The final Democratic presidential debate of the year is bringing seven 2020 candidates to the stage in California one day after the House voted to impeach Donald Trump for abuse of power and obstruction.

Facing off in Los Angeles on Thursday are the former vice president Joe Biden and senators Bernie Sanders and Elizabeth Warren; the South Bend, Indiana mayor, Pete Buttigieg; Senator Amy Klobuchar, the entrepreneur Andrew Yang and the billionaire environmental activist Tom Steyer.

Looming over the high-stakes debate are those who won’t be in attendance. The Democratic National Committee said candidates had to hit at least 4% in four national polls or at least 6% in two early-state polls in the weeks leading up to the event in order to qualify. The candidates also had to attract at least 200,000 donors.

That leaves no black or Latino candidates among the nearly all-white lineup of Democratic frontrunners. Senator Cory Booker and the former housing secretary Julián Castro both failed to qualify for the debate, and Senator Kamala Harris recently ended her campaign amid polling showing her far behind in California, her home state.

Also absent from the event will be Michael Bloomberg, the former New York City mayor and billionaire who made a late entrance into the race last month and has poured an estimated $13.5m into TV ads in California. Steyer, the other billionaire in the race, has spent roughly $1.6m on ads in the state.

The fifth presidential debate, which will take place at Loyola Marymount University, comes the same week that Trump has become the third president in US history to be impeached, prompting him to accuse Democratic leaders of a “war on American democracy”.

The debate is the first in California, a state that has become a leader of the resistance to the Trump administration’s agenda on immigration, the climate crisis, health care and other issues. In visits to the Golden State, the president has repeatedly attacked Democrats over the homelessness crisis, at one point complaining about homeless people taking up space on “our best streets, our best entrances to buildings”. Trump has repeatedly suggested he will push some kind of police crackdown on people living on the street.

The stakes on Thursday night are different for each candidate. Biden, who has been a frontrunner in the race, is probably trying to “stay steady and do no harm” and avoid any standout moments, said Jessica Levinson, a Loyola law school professor: “He has to retain the support he has.”

Klobuchar, who has been trailing in the polls, “has to do something different and something exciting”, the professor said. “She’s going to have to make a case that there’s a reason she’s still there.”

There may be a lot of attention and attacks on Warren, who has been steadily climbing in the polls, and the senator will probably want to show that she hasn’t peaked too soon and that her successes in recent months will be sustainable, Levinson said.

Some recent polls have shown Sanders ahead of Warren in California, and the two are expected to be competing for progressive voters in the state.

For Buttigieg, the debate comes after weeks of intense scrutiny surrounding his previous work with McKinsey, the controversial consulting company. Buttigieg is, however, polling well in Iowa and New Hampshire, the first states to vote in the primary season.

Despite spending millions on the race, Steyer has remained stuck near the bottom of the polls.

Most candidates just want to finish the debate with clips that cut through on social media, said Levinson: “The debates have really become auditions for viral moments … Did they have a breakout 30 seconds somewhere that we can play over and over?”

This could be critical given that the next debate won’t happen for another month and that Trump’s impeachment is likely to overshadow news about the primaries for some time.

But viral debate speeches may not matter much in the long term. One of the most memorable lines in the primary came Harris, California’s junior senator, who attacked Biden in June with a comment about her own personal experience with school integration when she was a child.

A labor dispute had threatened to derail the LA debate earlier in the week when the candidates announced they would boycott in support of a union planning to picket the Loyola campus the night of a debate. On Tuesday, the union, Unite Here Local 11, announced it had reached a tentative agreement with the campus food services contractor.