A new survey in Iowa suggests that one month out from the caucuses, President Trump is solidifying his lead in the Republican primary.

A new survey from NBC News, the Des Moines Register, and Mediacom found that Mr. Trump has expanded his lead over Governor DeSantis in the state since the last survey conducted by the pollster in October.

Now, Mr. Trump enjoys the support of 63 percent of likely caucus goers, up from 43 percent in October. Mr. DeSantis now enjoys the support of 19 percent of caucus goers, up from 16 percent in October.

The former ambassador to the United Nations, Nikki Haley, was the first choice of 16 percent of likely Republican caucus goers, the same level of support she had in October.

The survey, conducted by pollster J. Ann Selzer, also found that more voters have “made up” their minds about who they will support compared to October.

In the December poll, 49 percent of likely caucus goers said they had made up their minds, compared to 41 percent in October. Likewise, 46 percent now say that they could still be persuaded, compared to 54 percent in October.

At the same time, Mr. Trump’s supporters were more likely to have made up their minds than either Mr. DeSantis or Ms. Haley’s supporters.

Among supporters of Mr. Trump, 70 percent said they had made up their minds. Among Mr. DeSantis’s supporters, 30 percent had made up their minds. Among Ms. Haley’s supporters, 34 percent had made up their minds.

Most GOP caucus goers also don’t see Mr. Trump’s legal issues as a major liability, with 73 percent saying he can win regardless of legal challenges compared to 24 percent who say it will make it nearly impossible.

This is an increase since October when 65 percent said that Mr. Trump could win despite his legal challenges, and 32 percent said that they would make it nearly impossible.

Ms. Seltzer told NBC News that “the field may have shrunk, but it may have made Donald Trump even stronger,” calling Mr. Trump’s lead “commanding.” 

Ms. Selzer did caution, however, that the Iowa Caucuses are historically unpredictable and that “Everything that could happen has happened in this contest.”

The survey of 504 likely Republican caucus goers had a margin of error of plus or minus 4.4 points. Mr. Trump appears to be consolidating his lead in other early states as well.

At New Hampshire, a November survey by a group that has endorsed Ms. Haley, Americans for Prosperity, found that Ms. Haley trails Mr. Trump 25 percent to 40 percent there, with Mr. DeSantis in third with 11 percent.

In South Carolina, a December Trafalgar Group poll found that Mr. Trump maintains 49 percent support, with Ms. Haley and Mr. DeSantis enjoying 23 percent and 14 percent support, respectively.

In general election polling for the presidential election next year, Mr. Trump appears to be gaining momentum as well. A recent Wall Street Journal poll found that Mr. Trump leads President Biden by 4 points nationally, 47 percent to 43 percent.