Tuesday night’s Democratic presidential primary debate will be the largest ever, with 12 candidates on a single debate stage.

Here are 10 things to watch:

1. Joe Biden projecting strength in response to Trump attacks

Biden's initial response to President Trump's attacks as House Democrats move forward on an impeachment inquiry made some wonder if he is ready to take on Trump. Biden immediately brushed off Trump's suggestion that the former vice president pushed to fire a Ukrainian prosecutor who opened an investigation into a gas company that had his son Hunter Biden on the board. But his approach has gotten more aggressive in recent weeks.

"It’s way beyond anything I quite frankly thought he would do,” Biden said a few weeks ago.

Biden strengthened his offense against Trump in recent days and called for Trump's impeachment last week. But after lackluster performance in previous debates, he is under more pressure than ever to show that he can go toe-to-toe with Trump in a general election.

2. How Biden’s rivals handle Hunter ethics questions

Many Democratic presidential hopefuls — including Cory Booker, Kamala Harris, Beto O’Rourke — have said that they would not allow a son or daughter of their vice president or Cabinet member to serve on the board of a foreign company, as Hunter Biden did for a Ukrainian gas company while his father was president. Others, including Julián Castro and Pete Buttigieg, have refused to answer similar questions, arguing that the premise frames the issue on President Trump’s terms.

Biden maintains that he and his son did nothing wrong or illegal, but the former vice president’s pledge that no one in his family or anyone associated with him would serve on a foreign board highlights some Democrats' discomfort with the arrangement. Candidates are unlikely to bring up the issue unless prompted, but some may downplay previous statements and others may draw new ethics distinctions between themselves and Biden.

3. Bernie Sanders' health after heart attack

Tuesday’s debate will be Sanders’ first major campaign appearance since he suffered a heart attack two weeks ago and spent three days in the hospital. The 78-year-old Vermont senator indicated that he would scale back his campaign events and schedule after the incident, but then the next day, he walked back his statement and his campaign tweeted a video of Sanders swinging a baseball bat in his backyard, subtly arguing that he is healthy.

The oldest presidential candidate in the race is under pressure to show that he is healthy enough to be president. Sanders frequently hunches over and leans on debate lecterns, but his posture may be exaggerated if he is feeling bad or subdued if he makes a conscious effort to appear energetic.

4. Warren in the spotlight after poll surge

Massachusetts Sen. Elizabeth Warren surpassed Joe Biden in many state and national polls in recent weeks, prompting some analysts to name her the new front-runner. But with increased stature in the field comes greater scrutiny, and moderators and primary rivals could be tougher on her than in previous debates. Biden quipped last week that "we're not electing a planner," taking a swipe at Warren's "I've got a plan for that" mantra. Sanders drew a line between himself and fellow progressive Warren this weekend. "She is a capitalist through her bones. I'm not," Sanders said.

5. Who will Tulsi Gabbard attack next?

Hawaii Rep. Tulsi Gabbard did not qualify for the September debate, but she secured enough qualifying polls to make it back for the October round. In previous debates, Gabbard tore into competitor Ohio Rep. Tim Ryan for incorrectly saying that the Taliban attacked the United States on 9/11 and accused California Sen. Kamala Harris of keeping innocent people on death row. Tonight, she might take on another candidate or even the Democratic National Committee. Last week, Gabbard threatened to boycott tonight's stage, citing an "undemocratic" qualification process and calling the debates "commercialized reality television."

6. Tom Steyer’s debate debut

Billionaire businessman Tom Steyer will make his debate debut on Tuesday. He launched his campaign late, after the first two Democratic presidential debates had taken place, but managed to qualify for the October debate in part by spending millions of his own money on television and digital ads to secure individual donors and increase his name recognition in early voting states. The debate is his chance to argue against those who believe he bought his spot on the debate stage and make his first major national introduction to primary voters.

7. Buttigieg battles

South Bend, Indiana, Mayor Pete Buttigieg peeved primary rivals New Jersey Sen. Cory Booker and former Texas Rep. Beto O'Rourke on Monday with his opposition to confiscation of military-style weapons. He also took a swipe at Warren's anti-large donor strategy and has distinguished himself from Joe Biden in the past. Buttigieg is in fourth place in most national polls, so if those behind him want to move up, they may try to tear him down.

8. Harris comeback

California Sen. Kamala Harris shot up in the polls after attacking Biden for working with segregationist senators in the 1970s to oppose busing, but then steadily declined in the polls and lost momentum. Trump impeachment proceedings may be Harris' chance to showcase her prosecutor style that made many like her during the June debate, but falling flat will add to her troubles.

9. Klobuchar and Castro on thin ice

Minnesota Sen. Amy Klobuchar and former Housing Secretary Julián Castro are struggling to earn enough qualifying polls to make the November debate stage and need to make an impact to help prop themselves up in the crowded field. Castro warned in a fundraising email that he may drop out if he does not make the November debate and took heat for criticizing Obama-era immigration policies during the September debate.

10. Crowded stage

Twelve candidates debating on one stage will mark the largest-ever presidential primary debate. Time constraints mean that some candidates could get far less speaking time than in previous debates and add to campaigns' frustrations about the Democratic National Committee's debate design. It could also mean that any tense disagreements continue through candidate statements in post-debate interviews.