Biden gives a foreign policy speech in New York in July. Photo: Spencer Platt/Getty Images

DETROIT, Mich. — The biggest lesson Joe Biden learned from the first debate is that there are no rules of engagement at these things, and he's ready to throw down at tonight's debate, according to five senior campaign officials.

What to watch: Yes, he's going to keep contrasting himself with President Trump. But he's squarely focused on Sen. Kamala Harris, too, after the first debate in Miami.

  • "We’re not joking when we say he’s not going to let his record be mischaracterized," said one senior campaign official. "It’s not OK to label someone as a racist."
  • They were referring to Harris' line to Biden at the last debate that started with: "I know you're not racist, but ... "
  • "Some folks are willing to go places we didn’t think they’d go,” said another senior Biden campaign official, who said they were surprised by Harris' exchange with him because she's been friends with Biden for years.
  • His team maintains he won't make any personal attacks against other Democrats, but Biden himself has said he won't be as "polite" as last time.

Why it matters: Any time Biden has to spend defending his record from other candidates' attacks is less time he'll have to take on Trump — something he's been doing since he launched his campaign, signaling he views himself as the eventual nominee.

Between the lines: Although Harris saw a bump in polling after her spat with Biden, his team believes that was temporary.

  • "This is not a new dynamic," said one senior Biden campaign official. "You see candidates who rise and the balloon pops once there’s more information on that person."
  • After the Miami debates, Harris reached 20% in a Quinnipiac poll, but she's since leveled back out at around 11%.

Health care dominated last night's discussion, which Biden watched, and he plans to present that as one of the major differences between himself and Harris, as well as Sen. Bernie Sanders.

The bottom line: Biden might be ready for a fight, but Harris is surely not the only one to go after him and his record, and that could introduce new vulnerabilities he's not yet anticipating.

Go deeper: Democrats prepare for debate brawl with Biden.

Go deeper

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The big picture: Ocasio-Cortez was pressed repeatedly on policy differences between her and the more moderate Biden, including her opposition to fracking and support for Medicare for All. She responded that it would be a "privilege" and a "luxury" to be able to lobby a Biden administration on progressive issues, insisting that the focus right now should be on winning the White House.

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Illustration: Sarah Grillo/Axios

Celebrating Halloween and Día de los Muertos will be difficult and more isolated this year, but can still be done while minimizing harm to others.

Why it matters: Traditional door-to-door trick-or-treating, indoor parties, haunted houses, crowded cemeteries and communal candy bowls are all considered high-risk activities by the CDC.