WASHINGTON — A dozen Democratic presidential contenders will be lining up on the debate stage in Ohio on Tuesday night, as struggling candidates try to revive their campaigns and the two front-runners look to cement their primacy.

It's all taking place against the backdrop of what promises to be an extended discussion of the pending impeachment of President Donald Trump.

And some in this group won't be back for the next round in November when the qualification threshold is higher and which means it's suddenly become too late for Democrats to say it's early in the process.

Former Vice President Joe Biden and Massachusetts Sen. Elizabeth Warren are the far-and-away front-runners in most national polls — with Vermont Sen. Bernie Sanders alone in third and making his first campaign appearance since suffering a heart attack — and the rest of the field struggling to break into mid-single-digit territory.

South Bend, Indiana, Mayor Pete Buttigieg is in a better spot than most: he's polling at a clear fourth in both Iowa and New Hampshire — the first two states to vote — where Warren is in the lead and Biden and Sanders are in second and third.

They'll all be competing for attention with the impeachment investigation of Trump, which kicked into high gear over the Ukraine affair after the last Democratic debate in Houston in September.

With all that in mind, here are five things to watch during Tuesday night's CNN/New York Times debate at Otterbein University in the Columbus suburb of Westerville, Ohio.

1. Warren's a target

Her rivals have been increasingly aggressive in criticizing the Massachusetts senator in recent weeks.

Buttigieg ripped her small-donor fundraising strategy in an interview with SnapChat's Peter Hamby — even though Warren out-raised him by more than $5 million in the most recent quarter.

"We're not going to beat Trump with pocket change," he said.

And to paint her as less progressive, Sanders told ABC News that Warren is "a capitalist through her bones."

The question for these candidates — and the others looking for a leg up — is whether they will, individually or collectively, say it on the stage. But the pack may not be able to afford to sit back and let Warren deliver her message to voters without contradiction.

2. Biden on defense

It's far more likely that Democrats will show solidarity with Biden in the face of Trump's efforts to investigate him and his son, Hunter, than attack him over the conspiracy theory that led Trump to seek Ukraine's assistance.

But there's little chance Biden will escape the stage without having to answer questions about why his son was paid a reported $50,000 a month to represent a Ukrainian gas company when the former vice president was in office. He's sure to counter questions about his son with what he's already previewed — including a proposed ethics policy that would ban foreign government lobbying — and Hunter Biden's announcement that he won't work for any foreign-owned entities if his father's elected president.

Biden's answers may give Democratic voters a sense of whether they believe — as he has suggested — that Trump's effort to destroy him is evidence that he's the strongest Democratic candidate.

3. Impeachment

The top Democrats are uniformly in favor of impeaching Trump, but they arrived there in different ways and on different schedules.

Warren, for example, was among the first of the presidential candidates to issue a clear call for impeachment when she read former special counsel Robert Mueller's report.

But it was only last week when Biden said for the first time that the House should impeach the president and added Sunday, "I'm the reason there is impeachment going on."

It's clear where Democratic activists stand — they want Trump gone by election or congressional action — but the rest of the country hasn't reached the same conclusion. That creates tension points between the candidates gunning for the party's base and House Democratic investigators who are trying to portray their investigation in the least political light possible.

4. 'Trying to make news'

Usually, a low-riding candidate will try to advance by swinging for a rival on a top rung. But if the last few days are any indication, the new tactic among those fighting for survival is to knock each other out.

New Jersey Sen. Cory Booker, former Texas Rep. Beto O'Rourke and Buttigieg are among the contenders who have taken various swipes at one another, opening up lines of attack that can be repeated in the debate.

"They're trying to make news," Rebecca Katz, a veteran Democratic strategist, said. "They're all trying to stay relevant. It's unclear if this will help any of them get more votes."

5. Trump-bashing...

Outside the campaigns, some Democrats are worried that neither Warren nor Biden is the right candidate to beat Trump, and the candidates in the wide bottom tier will be looking to give voters a reason to give them a second look.

While the inclination may be to tear each other down, Adam Parkhomenko, a consultant who worked on both of Hillary Clinton's presidential campaigns, said that's the wrong way to appeal to primary voters.

"Attacking someone is a net negative," he said of intraparty warfare. "If people feel the need to attack, they should get up there and attack Trump."

CORRECTION (Oct. 15, 2019, 6:38 p.m.): A previous version of this article misstated how much former Vice President Joe Biden’s son Hunter Biden was reportedly paid per month to represent a Ukrainian gas company. It was around $50,000 a month, not $500,000.