After Iowa, candidates are refocusing their messages as Governor DeSantis and Ambassador Nikki Haley attempt to parlay middling performances in the Hawkeye State into wins in future competitions.

After a resounding victory for President Trump in Iowa, Ms. Haley is focusing her campaign messaging on the prospect of a rematch between Mr. Trump and President Biden, something most Americans are not looking forward to if the polls are to be believed.

A new ad for Ms. Haley in New Hampshire criticizes Messrs. Biden and Trump as “the two most disliked politicians in America. … Both are consumed by chaos, negativity, and grievances of the past.”

“I have a different style and approach. I’ll fix our economy, close our border, and strengthen the cause of Freedom,”  Ms. Haley says in the ad. “We need a new generation of conservative leadership to get it done.”

In a statement Tuesday, Ms. Haley said that “Americans have been very clear: they’re done carrying the baggage for two 80-year-old politicians of the past.”

She elaborated on her criticism during an appearance on Fox News, saying, “You’ve got 70 percent of Americans who don’t want to see a Trump-Biden rematch. The majority of Americans disapprove of both Trump and Biden.” 

A December 14 Associated Press and NORC poll found that 56 percent of Americans would be “very” or “somewhat” dissatisfied with Mr. Biden as the Democratic nominee, and 58 percent would be dissatisfied with Mr. Trump as the Republican nominee. 

Another 28 percent said they would be dissatisfied with Messrs. Trump and Biden becoming their parties’ respective nominees.

As Ms. Haley sharpens her criticism of Messrs. Trump and Biden ahead of the vote next week in New Hampshire — a state that will likely be make-or-break for her campaign — Mr. DeSantis is pivoting to focus on South Carolina and sharpening his criticism of Ms. Haley.

Mr. DeSantis stopped for an event in South Carolina Tuesday, before heading to New Hampshire Tuesday evening. Mr. DeSantis’s support has collapsed in New Hampshire in recent months.

Since the beginning of November, support for Mr. DeSantis has slipped to about 5 percent from about 10 percent, according to FiveThirtyEight’s polling average. Mr. DeSantis is polling better in South Carolina — at about 12 percent, according to FiveThirtyEight.

Apparently hoping to chip away at Ms. Haley’s support in New Hampshire and her home state of South Carolina, Mr. DeSantis criticized Ms. Haley for saying that she would next only debate either Mr. Trump or Mr. Biden.

“Nikki Haley is afraid to debate because she doesn’t want to answer the tough questions such as how she got rich off Boeing after giving them millions in taxpayer handouts as governor of South Carolina,” Mr. DeSantis said.

He added, “I won’t snub New Hampshire voters like both Nikki Haley and Donald Trump, and plan to honor my commitments. I look forward to debating two empty podiums in the Granite State this week.”

ABC News, which is hosting a debate alongside WMUR-TV at Saint Anselm College, has given Ms. Haley and Mr. Trump a 5 p.m. deadline on Tuesday to commit to the upcoming debate.

Mr. DeSantis’s renewed attacks on Ms. Haley drew criticism from one of his state’s  most prominent representatives in the House, Congressman Matt Gaetz, who responded to his statement in a post, saying, “It’s over man.”

Mr. Trump, in the wake of his victory in Iowa, is projecting strength ahead of New Hampshire, even though that state will likely be the venue of the most credible challenge to his primary bid in the entire contest.

“I want to congratulate Ron and Nikki for having a good, a good time together,” Mr. Trump said of his opponents in remarks after the caucuses. “We’re all having a good time together. I think they both actually did very well.”

In a statement, a spokesman for Mr. Trump’s super PAC, MAGA Inc., Alex Pfeiffer, said that Iowans sent a clear message that they wanted Mr. Trump to be the nominee, adding, “It’s now time to make him the next President of the United States.”

While Mr. DeSantis bet big on Iowa, Ms. Haley has invested in New Hampshire. If she is unable to credibly challenge Mr. Trump in the Granite State, the nomination will likely be all but locked up for Mr. Trump.

Polling, though, indicates that Ms. Haley is closer to defeating Mr. Trump in New Hampshire than Mr. DeSantis was in Iowa. A new survey from American Research Group found that Ms. Haley is now tied with Mr. Trump in New Hampshire, at 40 percent support each.

According to the poll, Ms. Haley enjoys a majority of support, 51 percent, among undeclared voters as well as 35 percent support among Republicans.

Mr. Trump, for comparison, enjoys 47 percent support among Republicans and 24 percent support among undeclared voters, who made up 32 percent of respondents to the American Research Group survey. In FiveThirtyEight’s polling average, Mr. Trump enjoys a lead in New Hampshire, with 44 percent support compared to 31 percent for Ms. Haley.