Donald J. Trump was outrageous. He was demeaning. He was even somewhat menacing, warning a female moderator that he could turn on her at any moment.

When confronted with his tendency to describe the women he dislikes as “fat pigs,” “slobs” or “disgusting animals,” he dismissively replied that neither he nor the United States “have time for political correctness.”

After he thoroughly rattled the Republican presidential field and emerged as its singular vexation in the 2016 campaign, the question hovering over Mr. Trump, the developer turned reality TV star turned candidate, was whether he would adopt the measured and diplomatic manner of a plausible president for Thursday night’s debate.