LOS ANGELES — Fighting for attention in the twin shadows of President Donald Trump's impeachment and Christmas, seven of the remaining candidates for the Democratic presidential nomination will meet here Thursday night for the second-to-last debate before the Iowa caucuses.

The quiet nature of the race seems to have tested the patience of the candidates, and they've been a little more agitated of late — more willing to take shots at each other, both veiled and blatant. That could spill into more open warfare Thursday because they know they are running out of chances to broadcast their cases before the first votes are cast.

"For all candidates, this debate is the beginning of the closing argument," said Adam Green, co-founder of the Progressive Change Campaign Committee, which has endorsed Sen. Elizabeth Warren of Massachusetts.

There hasn't been much poll movement at the national level in recent weeks, with former Vice President Joe Biden maintaining a pared-down lead at 27.8 percent in the Real Clear Politics average of surveys, followed by Sen. Bernie Sanders at 19.3 percent, Warren at 15.2 percent and South Bend Mayor Pete Buttigieg at 8.3 percent. The one change: former New York Mayor Michael Bloomberg, a late entrant into the race, is regularly polling around 5 percent, putting him ahead of other candidates who have been campaigning for the better part of the year.

Bloomberg won't be on the debate stage due to party rules requiring a combination of donor counts and polling to qualify, nor will Sen. Cory Booker of New Jersey or former Housing and Urban Development Secretary Julián Castro. As a result, the only nonwhite candidate participating is political newcomer Andrew Yang, who will be joined by the four front-runners, along with billionaire Tom Steyer and Sen. Amy Klobuchar of Minnesota under the bright lights.

Here are five things to watch for at the debate, which will be co-hosted by Politico and PBS NewsHour at Loyola Marymount University and starts at 8 p.m. ET/5 p.m. PT.

Who handles impeachment best

All of the candidates at Thursday's debate are running to get rid of Trump — but only three of them stand to be the equivalent of jurors in his Senate trial.

With Speaker Nancy Pelosi, D-Calif., holding onto the articles of impeachment — at least for now — it's not clear when the trial would happen.

Whatever happens in Washington, the 2020 candidates have to "talk about this in a way that not only connects with primary voters but also connects with general [election] voters," said Rodell Mollineau, a Democratic strategist and partner at the public relations firm ROKK Solutions.

Three Musketeers

As the race has worn on, three of the front-runners have become more at ease fighting openly with each other — Warren, Buttigieg and Biden — while the fourth, Sanders, has never had much compunction about scrapping.

In September, Buttigieg called Warren "extremely evasive" on the details of her version of "Medicare for All." Biden has accused Buttigieg of swiping his health care plan. And Warren put enough pressure on Buttigieg to open up his fundraising program that America now knows he recently raised money in a wine cave.

The back-and-forth among their teams and their supporters is typically more direct and ferocious than the debate-stage tussling by the candidates, but that could change Thursday night as the stakes get higher and the window before the caucuses begins to close.

Bernie's free ride

Sanders is an ideological outlier among the candidates — a self-described democratic socialist — and he's cornered the market on about one-fifth of the party's voters. Normally, that might make him a target for attacks from rivals looking to break up his bloc.

But Biden benefits from having Sanders in second place because it means that Warren is not in that slot. Both Biden and Buttigieg stand to gain if Sanders were to drop out of the race at some point because many of his die-hard supporters have become hostile to Warren.

Warren and Sanders, both of whom have been trying to move their party to the left, are most likely to succeed in doing that if both can qualify for delegates in states and congressional districts across the country. If one of them beats up on the other, there's less chance of that happening. Look for Warren not to fight with Sanders, either, giving him a free ride from his peers in the lead pack.

Klobuchar has been inching up in the polls in Iowa in recent weeks, moving clearly into a distant fifth place. She's been tough in debates and unafraid to deliver a sharp rejoinder to a rival. But time isn't her ally in this race. She's running out of chances to bring in huge money from across the country, and she has every incentive to try to expose the weaknesses of her competitors. Keep an eye out for Klobuchar keeping an eye out for her opportunity to strike.

Reason for being

Steyer was the billionaire in the race who pushed for impeachment. Now, the House has impeached Trump, and fellow billionaire Michael Bloomberg is dumping hundreds of millions of dollars into his own campaign. Of late, Steyer's been running ads about term limits, which would require a constitutional amendment — but not a president's signature. The question Thursday night: whether he has a ready explanation for why he's running.