As Nikki Haley stepped to the podium Saturday night, the bravado she had embodied after losing in New Hampshire a month earlier was gone. Her expression was somber and, for a moment, she appeared to be edging toward withdrawing from the race for the Republican nomination.

“Our country will fall apart if we make the wrong choices. This has never been about me or my political future. We need to beat Joe Biden in November,” she said, as her audience held its breath.

Finally, she pivoted: “I don’t believe Donald Trump can beat Joe Biden.”

It was a remarkable corrective from Jan. 23, when she spun her 43 percent of New Hampshire’s vote from defeat into a kind of victory and vowed to beat Mr. Trump in her home state of South Carolina.

And though Ms. Haley similarly resolved to stay in the race on Saturday, her fortitude now looked more like stubborn grit and determination than upbeat confidence.

Mr. Trump delivered his own corrective on Saturday night. In New Hampshire, his victory speech had displayed all the grace and decorum of a professional wrestling show, down to mocking Ms. Haley’s dress and taunting her over losing. And he threatened that anyone who donated to her campaign would henceforth be “permanently barred from MAGA,” referring to his “Make America Great Again” movement as if it were one of his private golf clubs.

In Columbia, S.C., Mr. Trump didn’t even mention the name of Ms. Haley, his last major opponent — not exactly gracious, but not insulting either. Instead, he thanked his allies, coming closest to uttering an insult only when he invited Senator Lindsey Graham to say a few words by noting that he was “a little to the left” of the crowd, as his supporters booed their state’s senior senator.