Governor DeSantis is losing ground in the latest Fox Business poll, with his campaign trying to hold on to its second-place spot in the GOP field. Senator Scott and businessman Vivek Ramaswamy, meanwhile, appear to be catching up. 

Mr. DeSantis — long regarded as the prime alternative to President Trump for Republicans — has been struggling to make headway against Mr. Trump since his own campaign announcement.

Now, Mr. Scott, who has been gaining support among some major Republican donors in recent weeks, is catching up to Mr. DeSantis in the polls. A Fox Business poll in Iowa shows Mr. Scott trailing Mr. DeSantis in the state, 11 percent to 16 percent.

As a second-choice candidate, Mr. Scott polled at 14 percent. Mr. DeSantis, for comparison, was the second choice of 34 percent of GOP primary voters. Mr. Trump still dominates the field in Iowa, polling at 46 percent among likely GOP primary voters.

“Scott has a decent hand in Iowa,” pollster Chris Anderson said in a statement. “Nearly nine in ten caucus-goers are open to him, and he is drawing about equally from moderate Republicans as from the most conservative, meaning different types of voters are seeing things they like in him.” 

The poll of 806 likely caucus-goers had a plus or minus 3.5 point margin of error. The poll comes just days after another survey showed a different competitor, Mr. Ramaswamy, gaining on Mr. DeSantis.

A Kaplan Strategies survey released last week found Mr. DeSantis and Mr. Ramaswamy were tied at 12 percent support each, while Mr. Trump leads at 48 percent.

“Ramaswamy outperformed six other hopefuls by more than double, marking a significant surprise in this poll,” pollster Doug Kaplan said.

Mr. Kaplan predicted that the field would eventually winnow to three major candidates in the primary season and that supporters of the candidates that drop out “will either return to Trump or rally behind rising stars like Ramaswamy or DeSantis.”

As Mr. DeSantis works to keep his second place spot, Mr. Trump dominates the Republican field, carrying 50.8 percent support in FiveThirtyEight’s average of polls to Mr. DeSantis’s 18.9 percent.

A recent HarrisX poll conducted with Harvard’s Center for American Political Studies also found that Mr. Trump would win a head-to-head primary matchup against both Mr. DeSantis and Mr. Scott.

Against Mr. DeSantis, Mr. Trump would carry 63 percent of the vote to Mr. DeSantis’s 37 percent. Against Mr. Scott, Mr. Trump would carry 71 percent compared to Mr. Scott’s 28 percent.

The same poll found that Mr. Trump would be favored in a matchup against President Biden, leading him 45 percent to 40 percent, with 16 percent of voters undecided.

Other recent general election polling has suggested that Mr. Biden would be favored to win in the general election, with a Monmouth survey released last week finding that even in a three-way race between Mr. Biden, Mr. Trump, and Senator Manchin, Mr. Biden would be the favorite.

In the three way race scenario, Mr. Biden carried 40 percent support, Mr. Trump carried 34 percent support, and Mr. Manchin carried 16 percent support.

“We are still very much in the realm of hypotheticals, where voters’ assessment of their actual behavior can be unreliable,” Monmouth University Polling Institute director Patrick Murray said. “However, the more concrete you make an alternative to the major party candidates, the less attractive it becomes.”

A surprising result of the HarrisX poll is that attorney Robert Kennedy Jr. enjoys a higher favorability rating than three major presidential candidates.

Mr. Kennedy’s favorability rating was 47 percent, according to the survey. For comparison, Mr. Trump’s was 45 percent, Mr. DeSantis’s was 40 percent, and Mr. Biden’s was 39 percent.