Gov. Kristi Noem of South Dakota and the entrepreneur Vivek Ramaswamy tied for the top choice to be former President Donald J. Trump’s running mate in a straw poll on Saturday at a prominent gathering of conservative activists.

The straw poll, at the Conservative Political Action Conference, was the first time in years that a question about whom Republicans should pick for vice president had overshadowed one about the presidential nominee in the survey of attendees.

That was partly because Mr. Trump won the presidential poll, as expected, in a landslide over Nikki Haley, beating her by 94 percent to 5 percent. The last time Mr. Trump was not the top choice for the White House among CPAC attendees was in 2016, when Senator Ted Cruz of Texas finished first.

The straw poll, which provides one measure of enthusiasm on the far right and is not intended to be predictive, was announced at the end of the four-day CPAC gathering outside Washington. The attention on the vice-presidential question was notable because Mr. Trump is still fending off a challenge for the Republican presidential nomination by Ms. Haley, the former governor of South Carolina. He has won the party’s first several nominating contests and easily defeated Ms. Haley on Saturday in her home state.

Several Republicans viewed as contenders to be Mr. Trump’s running mate gave speeches at the event. They included Representative Byron Donalds of Florida on Thursday; Ms. Noem, Senator J.D. Vance of Ohio and Representative Elise Stefanik of New York on Friday; and Kari Lake, an Arizona Senate candidate, on Saturday. Mr. Ramaswamy spoke on both Friday and Saturday.

Ms. Noem and Mr. Ramaswamy each garnered 15 percent of the vote in the straw poll. Former Representative Tulsi Gabbard of Hawaii, who ran for president as a Democrat in 2020 but has since left the party to become an independent, was third with 9 percent, followed by Ms. Stefanik and Senator Tim Scott of South Carolina with 8 percent each.

Mr. Vance, whom CPAC attendees choose as their favorite senator, received 2 percent in the vice-presidential question, behind Tucker Carlson, a former Fox News anchor, and Robert F. Kennedy Jr., the political scion of a Democratic family who is now running for president as an independent.

“It feels like I’m the only one who isn’t running for vice president,” said Tom Fitton, the president of the conservative group Judicial Watch, who spoke at the conference. “Although — who knows what will happen.”

Charles Romaine, 75, a retiree in Silver Springs, Md., said he had arrived at his first CPAC this week supporting Ms. Stefanik as Mr. Trump’s No. 2, but changed his mind to Ms. Noem after hearing her speak on Friday.

He said that Ms. Noem’s speech was energetic and that he liked her opposition to health restrictions during the coronavirus pandemic and her support for sending National Guard troops to the southwestern border.

“She has had real authority as governor and she’s used it,” Mr. Romaine said. “That’s important experience to be vice president and, maybe, someday, president.”

James Ong, 20, a college student in Washington, D.C., said he had supported Mr. Ramaswamy, the 38-year-old businessman, as Mr. Trump’s running mate because he could appeal to younger voters whom the older presidential candidates in both parties might struggle to win over.

“America First is about America’s future, not just Trump, and Vivek can carry on that legacy,” Mr. Ong said.

Mr. Trump’s third presidential campaign will be his first without former Vice President Mike Pence on his ticket. The two men parted ways politically after Mr. Pence refused to help Mr. Trump overturn the 2020 election.

Behind the scenes, Mr. Trump has informally discussed potential running mates with advisers, and his team has weighed the risks and rewards of potential contenders.

Publicly, the former president has offered conflicting thoughts on the role. He said last month that he knew whom he would pick as his running mate, but later said he had not decided.

His campaign, meanwhile, has leaned into the anticipation.

His team has emailed and texted supporters with more than two dozen fund-raising solicitations this month designed to look like surveys about whom Mr. Trump should pick. The questionnaire mostly asks about various characteristics for a possible vice president but does not offer any specific names.