In the first surveys following the first Republican primary debate at Milwaukee on Wednesday, businessman Vivek Ramaswamy is up and Governor DeSantis is down, even in Florida.

In a survey by McLaughlin and Associates, Mr. Ramaswamy overtook Mr. DeSantis as the second-place candidate behind President Trump, who maintains a 38-point lead over Mr. Ramaswamy.

The poll found that Mr. Trump enjoys 51 percent support among GOP voters, Mr. Ramaswamy is at 13 percent, and Mr. DeSantis is at 9 percent. Vice President Pence, Senator Scott, and Governor Christie are tied at 4 percent support, while Governor Haley is at 3 percent and all other candidates received 1 percent support or less.

Since the July poll, the survey found that Mr. Trump has lost 1 point, while Mr. Ramaswamy has gained 5 points, and Mr. DeSantis has lost 4 percent of his support.

In a head-to-head matchup between Messrs. Trump and DeSantis, Mr. Trump enjoyed the support of 72 percent of the Republican voters while Mr. DeSantis was at 28 percent, a 2-point shift in favor of Mr. Trump since the July poll.

Republicans who watched the debate did report thinking that Mr. DeSantis had a strong performance, even if they thought Mr. Ramaswamy did better.

An overnight JLP and Daily Mail survey found that, of Republicans who watched the debate, 28 percent said that Mr. Ramaswamy had the best performance; another 27 percent said Mr. DeSantis had the best debate, and 13 percent said Mr. Pence did so.

An Ipsos survey of Republican voters who watched the debate, done in conjunction with FiveThirtyEight and the Washington Post, found similar results.

The Ipsos survey found that 29 percent of respondents thought Mr. DeSantis had the best performance, followed by Mr. Ramaswamy at 26 percent and Ms. Haley at 15 percent.

Messrs. DeSantis and Ramaswamy also saw 4.5-point and 5.5-point increases in the proportion of debate watchers considering them after the debate, respectively. Mr. Trump was the only candidate to see this score decrease, to 61.4 percent from 66.2 percent.

The breakout performance of the night may have been by Ms. Haley, who saw the proportion of Republicans who say they are considering supporting her rise dramatically, to 46.7 percent from 30.2 percent among debate watchers.

As Mr. DeSantis’s numbers deflate in the national polls, he is also losing ground to Mr. Trump in Florida, according to a survey of state voters conducted by Victory Insights between August 21 and 23.

The survey found that, since the pollster’s last survey conducted in May, Mr. DeSantis has seen a dramatic collapse in support in his home state for the 2024 presidential race.

In May, Messrs. Trump and DeSantis were statistically tied at about 38 percent support in Florida. Now, Mr. Trump enjoys 58.8 percent support, and Mr. DeSantis is at 22.5 percent in his home state.

“On the full ballot of Republican contenders, Trump’s lead jumps to a whopping 36 points,” pollster Ben Galbrailth said. “The data clearly indicates a massive increase in support for Trump over DeSantis in the last few months.”

Mr. Trump also leads in a head-to-head matchup versus Mr. DeSantis in Florida, enjoying 57.4 percent support to Mr. DeSantis’s 30.1 percent.

The pollster also found that a significant portion of voters who supported Mr. DeSantis for governor would not back Mr. Trump in the presidential race, with 10.3 percent saying that they would vote for President Biden in the general election and 16.4 percent saying they are undecided about whether they would support Mr. Trump or Mr. Biden.

Although it was limited to the state of Florida, the Victory Insights survey found that Mr. Ramaswamy is a favorite for the vice presidency among GOP voters, enjoying 22.4 percent support in that arena.

After Mr. Ramaswamy, a TV host, Kari Lake, was at 12.9 percent, Mr. Scott was at 12.3 percent, and Congressman Byron Donalds enjoyed 10.4 percent support for the vice presidency.