MADISON, Wis. — Republicans gathering for the Wisconsin state party convention Saturday will vote on whether to endorse Leah Vukmir or Kevin Nicholson in the closely watched race for U.S. Senate, a decision that's crucial to Vukmir in solidifying her as the preferred choice of conservative activists.

It would also provide a much-needed counterpunch to the millions flowing in from outside groups for Nicholson, a former Democrat and decorated Marine who is casting himself as the type of political outsider that's needed in the Donald Trump era.

Endorsement brings state party resources like donor lists, field staff and money. It doesn't anoint the nominee; voters will decide that in the Aug. 14 primary, with the winner advancing to take on Democratic Sen. Tammy Baldwin.

Nicholson has all but conceded endorsement to the better-known and establishment-supported Vukmir. He told supporters last month that Vukmir was too cozy with the "political establishment" and it'll be a defeat if she gets less than 85 percent of the vote.

Vukmir, a 15-year veteran of the Legislature and close ally of Gov. Scott Walker, has said she's confident she will get the endorsement. She's been working hard across the state to shore up her support, but Nicholson too has been courting delegates and may be able to shave off enough to deny Vukmir the 60 percent she needs to win.

Vukmir has "staked her entire campaign on the need to win a convention in May," said Nicholson's spokesman Brandon Moody. Moody said Nicholson is more focused on winning the primary and then defeating Baldwin.

Vukmir said in a statement that she's put 61,000 miles on her car visiting every county in the state courting delegates. She said "they want someone who has stood with them and with Gov. Walker."

The importance of the endorsement should not be discounted, said Republican Sen. Ron Johnson. He captured it in 2010, just a week after entering the race, providing him with momentum and grassroots support as he went on to defeat Democratic Sen. Russ Feingold.

"For me, it was absolutely crucial," Johnson said.

Ignoring the activists who vote on the endorsement is "not a formula for success," he said.

"Our success — Scott Walker's success, my success, those of us who won statewide — is because of the state party structure," Johnson said.

While Walker and Johnson both won endorsement in 2010 on their way to statewide victories, candidates have won without it, too.

Tommy Thompson, the former governor who ran for Senate in 2012, came in third place in the endorsement vote. He went on to win the primary while the candidate who got the most endorsement votes came in fourth. Thompson then lost the general election to Baldwin.

Thompson, who is not endorsing in the primary, said the endorsement vote is more important for candidates like Nicholson and Vukmir who have never run statewide before.

"If Leah wins the endorsement, it will be a one-day story in the press but it will mean a lot more at the county level as she goes across the state," Thompson said. "She will have a built-in campaign infrastructure."

Thompson's senior adviser in the 2012 race agreed with the importance of the endorsement — to a point.

"Any advantage you can put on your side of the campaign is going to be helpful," Brian Nemoir said.

While Nemoir said no one wants to lose the vote, "It's hard to make the case it will make or break the campaigns of either candidate."

Vukmir is largely following the model of Johnson and Walker in their pursuit of the endorsement, while Nicholson is distancing himself from the party establishment. It's a similar argument that Texas Sen. Ted Cruz made on his way to winning the Wisconsin primary in 2016 and that Trump made in taking the state in the fall.

But the anti-party argument did not work for former congressman Mark Neumann, who took that approach in 2010 when he ran for governor against Walker and again in 2012 when he ran for Senate. Neumann, who finished second in the 2012 Senate endorsement vote, has donated to Nicholson's campaign.

No matter the outcome of the vote, Johnson said he hoped that Vukmir and Nicholson avoid a repeat of the bruising 2012 primary that left Thompson broke and damaged in the public eye before taking on Baldwin.

That means if it becomes clear that victory is inevitable for one candidate — not just through the endorsement vote but a multitude of measurements like polling and fundraising — the other would step aside, Johnson said.