His rivals, who have been piling on in recent days, will try to rattle him by attacking his record, campaign aides have told POLITICO. His own team worries that an unsteady showing alongside practiced candidates could stall his momentum and swallow his gains.

“We are expecting that he is going to have a lot of attention on him — he’s going to be attacked,” a Bloomberg official told POLITICO, noting that it would be his first debate since 2009. The official, who declined to speak on the record, pointed to the other candidates who’ve had months of practice in eight debates and numerous forums and “have gotten better as it’s gone on.”

So Bloomberg has spent weeks getting ready.

“You know me: I like a fight, and so I think it’d be fun to go and compete,” he said during an interview in Detroit earlier this month. Likening it to his sometimes contentious press conferences during his 12 years as mayor, he added, “I always thought that was fun to joust.”