For all of the high-minded hopes about discussing the future of the party and the country, the Republicans acknowledged that the most attention-grabbing moments came when candidates clashed or made an exceptionally passionate point. Their advice to Democrats now: Be ready to jump in with your message every time the spotlight comes to you, rather than complaining about rules or the amount of time you get to speak.

“You have to decide beforehand, when you go up there, what is the message you want to convey, and to use whatever questions you get to convey that message,” Mr. Christie said.

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Tim Miller, who was the communications director for former Gov. Jeb Bush of Florida in 2016, also argued for stockpiling a few memorable one-liners, whether tied to another candidate or about the opposing party — “something people are going to play on TV the next day, something that’s going to get the crowd going.” With so many people onstage, he said, candidates should be careful not to get lost. Besides an embarrassing moment, he warned, the worst possible outcome is “being the person who’s not talked about.”

Mr. Miller pointed to Mr. Bush’s reference to Mr. Trump as the “chaos candidate.”

“That was a rehearsed, practiced line, and he delivered it well, and it was a new critique of Trump,” Mr. Miller said. “It gave something for people to talk about.”

At a number of political gatherings in the early months of the campaign, Democratic candidates have sought to emphasize party unity. But with so many candidates desperate to make an impression, they should brace for ugly, too.

“When there are 10 candidates, some of whom are already on life support, you better be prepared for someone to come off the rope with a chair to knock you out in the first round,” said Alex Conant, who was the communications director for Senator Marco Rubio of Florida in the 2016 primary.