DETROIT, Mich. — On tonight's debate stage, Beto O'Rourke is "getting back to the candidate who has courage in his convictions and in what he believes," according to one of his senior campaign aides.

Why it matters: He's trying to boost his fortunes by resetting his campaign — again. He's been struggling since May, and he flopped at the first debate in Miami. Tonight could be a do-or-die moment for Beto, but he's not the only one to watch.

Beto went into the first debate hoping for a reboot.

But he ultimately helped lift other candidates, like Julián Castro, who took him to task on immigration. Beto had no defense.

"Compared to last time, he’ll be ready for others who might want to use him to make their own points," a Beto campaign aide told Axios.

He'll talk a lot about immigration and health care, per the O'Rourke campaign, drawing distinctions between Medicare for All and what he's proposed as "Medicare for America."

What else to watch in tonight's debate: Whether anyone goes after Joe Biden, even though he's not on stage.

That didn't happen on the first night in Miami, but the gloves are off this time.

Bernie Sanders has been ramping up his attacks against Biden recently, especially over health care. “[U]nfortunately, he is sounding like Donald Trump. He is sounding like the health care industry in that regard,” Sanders told the New York Times, speaking of Biden.

Sanders and Elizabeth Warren will be standing next to each other tonight, and while they've so far been friendly, that could change.

Nina Turner, the national co-chair of Sanders' 2020 campaign, said on MSNBC today that she expects both of them to go after the "neoliberal wing of the Democratic Party," meaning more moderate candidates in the field, like John Delaney or Tim Ryan.

Warren has enjoyed, for at least 3 months, being the person with the big plans and the bold ideas. She’s been able to ride that to second or third place in the polls, but watch for how Sanders tries to take credit for pushing the party to the left.

"Bernie and Warren have played nicely," said Aimee Allison, Democratic strategist and founder of She the People, "but there are important differences between all of them, and this is the debate to see that out."

President Trump has made socialism the lynchpin of his position against 2020 Democrats. If the moderators ask about socialist policies, expect Sanders to be the sole person embracing that; the others will squirm to show the ways in which they’re not socialists.

Six candidates on stage tonight haven't yet qualified for the September debates in Houston.

That means tonight is a do-or-die moment for Marianne Williamson, Tim Ryan, Amy Klobuchar, John Hickenlooper, John Delaney and Steve Bullock.

It's hard to raise money and climb in the polls if you can't get a breakout moment in the debates, so watch for how those folks try to create one for themselves.

Klobuchar's campaign told me that while she's still introducing herself to the American people, she will draw clear contrasts between herself and others like Sanders and Warren.

"She's not going to promise everyone the world, and it’s important we’re not doing that," said one of her campaign aides.

Race and racism have dominated national conversations in the last few weeks, thanks to Trump's continued racist attacks against Democratic lawmakers, including 4 women of color informally known as the Squad: Reps. Alexandria Ocasio-Cortez (N.Y.), Ilhan Omar (Minn.), Ayanna Pressley (Mass.) and Rashida Tlaib (Mich.).

Several Democratic strategists I spoke with said they'd be shocked if these issues didn't come up for discussion tonight and tomorrow.

"Trump has made race central to the 2020 election," Democratic strategist Alaina Beverly said. "I'm expecting and hoping they’ll say they stand with the Squad and stand with the diversity that the Squad represents, and embrace that as part of who the Democratic Party is."

But don't forget: Tonight's debate lineup features only white candidates.

Go deeper: Democrats prepare for debate brawl with Joe Biden