For Mr. Buttigieg, the strategy of going on the attack has largely worked. He didn’t cement his place in the top tier of the Democratic primary until he became more aggressive.

His aides say they have been successful in drawing Ms. Warren and Senator Bernie Sanders of Vermont into advantageous policy fights on free college and eliminating private health insurance, which Mr. Buttigieg opposes. And in Iowa, where Democrats famously say they don’t like negative campaigning, Mr. Buttigieg has not been punished for going on the attack — in fact, he has been rewarded.

But on Thursday, Mr. Buttigieg may be in for some payback. As the polling leader in Iowa, the first caucus state, he is likely to draw substantial fire from most of the six other Democrats debating onstage at Loyola Marymount University in Los Angeles.

If so, it would be Mr. Buttigieg’s first experience as the primary punching bag, an honor that has gone to Mr. Biden and Ms. Warren in previous debates.

During the November debate, a sleepy affair in Atlanta, Mr. Buttigieg largely got a pass from his rivals. But since then he has been the subject of attacks from Ms. Warren on his fund-raising practices, from Mr. Sanders on health care policy and from other Democrats skeptical of his post-college work for the McKinsey consulting firm and his ability to appeal to African-American voters.