National Republicans appear to be going all-in on an Army veteran, Sam Brown, as their preferred candidate for Senate in Nevada, despite reservations from some in the party over his popularity in the state.

The chairman of the National Republican Senatorial Committee, Senator Daines, is hosting a fundraiser for Mr. Brown at Washington, D.C., on September 13, and at least 20 Republican senators are scheduled to attend.

The event is a show of support for Mr. Brown, a candidate who lost the nomination in 2022 to an acolyte of President Trump, Attorney General Adam Laxalt, by about 21 points. Mr. Laxalt went on to lose the general election.

In 2022, Mr. Trump and other Republicans like Governor DeSantis helped propel Mr. Laxalt — who was the frontrunner for most of the race — to the nomination. 

In his campaign announcement in July, Mr. Brown criticized President Biden and his potential general election opponent, Senator Rosen, saying they’ve “abandoned Nevada and divided America with extreme policies to satisfy special interests in Washington.”

Before Mr. Brown is able to campaign against Ms. Rosen, he will have to make it through a primary against two loyalists of Mr. Trump.

Mr. Brown’s current chief primary opponent is a businessman and state assembly member who lost a race for secretary of state in 2022, Jim Marchant. Like Mr. Laxalt, Mr. Marchant is aligned with Mr. Trump. Mr. Brown also appears likely to face another challenger from Mr. Trump’s wing of the party, Ambassador Jeffrey Gunter.

Although Mr. Brown was an ally of Mr. Trump in 2020, he has so far been cautious about aligning himself with the former president, something for which Mr. Brown’s opponents have been quick to criticize him. It’s clear, too, that Democrats are looking to stoke division within the party.

“With the entrance of Mitch McConnell’s handpicked candidate Sam Brown, Republicans are in for a brutal and messy primary that will expose their deeply flawed candidates as out of touch with hardworking Nevadans,” a Nevada Democratic Party spokeswoman, Johanna Warshaw, said in a statement.

Mr. Brown’s campaign has deflected criticisms concerning the evolution of his relationships with Mr. Trump and Senator McConnell.

“Sam’s message has been consistent throughout: He wants to change Washington and put people first,” Mr. Brown’s campaign said in a statement. “The difference this time is that other people are recognizing he is the best candidate to do that.”

Ahead of the 2022 race, Mr. Brown had been critical of Mr. McConnell’s leadership and had used Mr. McConnell’s endorsement of Mr. Laxalt against him during the campaign.

Although Mr. McConnell has not formally endorsed Mr. Brown, the NRSC is closely aligned with Mr. McConnell, and Mr. Brown, being the favored candidate of the committee, will likely be used against him.

In conversation with the Nevada Independent, a Nevada GOP strategist, Jeremy Hughes, said that he expects that Democrats may employ a strategy of propping up Mr. Brown’s opponents in order to try to weaken him in the general election.

“The biggest contributors to Marchant’s campaign will be the Democrats when they try to promote him in April and May of next year,” Mr. Hughes said. “That’s clearly what they’re going to do.”

After the NRSC-hosted fundraiser at Washington, D.C., in September, it may be difficult for Mr. Brown to position himself as an outsider again or continue to claim that his relationship with the entrenched GOP leadership hasn’t shifted since 2022. 

While perceptions of being supported by political insiders might not affect the outcome of the primary race in Nevada, it could matter in the general election, where contests are often decided by razor-thin margins. In 2022, Senator Cortez Masto defeated Mr. Laxalt by less than a point, 48.81 percent to 48.04 percent. The Cook Political Report currently rates the race as “lean” Democratic.