What to watch for in tonight's Democratic debate

WESTERVILLE, Ohio — Mayor Pete Buttigieg has gone from playing the adult in the room to starting the food fight, calling out Beto O'Rourke, Elizabeth Warren and Bernie Sanders by name this week.

Why it matters: Conversations with various campaign aides suggest he won't be the only one throwing punches tonight at the fourth Democratic debate here.

The big picture: There are 12 candidates on stage tonight, and the field needs to winnow for voters' sake. Democrats know that impeachment is sucking up all the oxygen. And if you want to make it to the November debate — which has even tougher qualification thresholds — you have to try something.

The state of play: Buttigieg's campaign started running a digital ad today calling out Sanders and Warren (by name!) for their support of Medicare for All.

• His campaign says his "Medicare for All Who Want It" plan "would give [voters] the option to choose the plan that's right for their them."
• This matters because he's the first Democrat to put money behind an ad attacking his fellow Democrats this explicitly.

Mandatory buybacks for assault weapons is splitting the field. O'Rourke has already clashed with Buttigieg over the idea, which O'Rourke supports.

• “I get it. He needs to pick a fight in order to stay relevant,” Buttigieg told Snapchat's Good Luck America host Peter Hamby yesterday. He also said mandatory buybacks amounts to a "confiscation" of these weapons.
• That prompted O'Rourke, Kamala Harris and Cory Booker to pile on the South Bend mayor on Twitter. A Booker campaign aide said the New Jersey senator is trying to find a moment tonight, much like everyone else.

Impeachment is having its moment. That will put Biden at the center of these discussions, with the moderators more than likely asking him questions about his son's business in Ukraine — especially after Hunter Biden's interview with ABC News that aired today.

• Biden will do his best to shift the spotlight back to President Trump. We saw a preview of this yesterday when his team unveiled an ethics plan, arguing Trump has created the "most corrupt administration in modern history."

But the real impeachment wild card here is Tom Steyer — a billionaire and Democratic activist who will join the other candidates on stage for the first time tonight.

• Watch for him to go after other Democrats over when they came out in support of impeachment and why it took some of them so long.
• "Impeachment is a good example of why Tom doesn’t make decisions based on polling," said Heather Hargreaves, his campaign manager. "He was for it when it wasn't polling as high as now because he knew it was the morally right thing to do."

Don't expect Warren to engage in the drama, just as we've seen her retreat in past debates while her colleagues duke it out. She's taken a more leisurely approach to debate prep.

• She went for a walk this morning, as part of her debate-day routine, and met with the winner of her contest to attend the debate, per a Warren campaign aide.

One big question: Why is Rep. Tim Ryan still running? Ohio is his home state and he didn't qualify for the debate. He didn't qualify last time in Houston, either. And things are looking bleak for the November debate, too.