Finding Republicans unhappy with Sen. Dean Heller isn’t too difficult these days.

From radio host Hugh Hewitt to rank-and-file Republicans upset with Heller’s chilly relationship with President Donald Trump — who issued a thinly-veiled threat to Heller at a luncheon this week — questions have begun swirling as to whether Heller could be vulnerable to a primary challenge.

“He’s got to get his act together,” activist Ron Solomon said at a recent meeting of the Clark County Republican Party, criticizing a recent Heller press conference where the senator seemed troubled by an Obamacare repeal bill. “When he stood up there with (Gov. Brian) Sandoval in the Grant Sawyer building three weeks ago, he sounded like he had Nancy Pelosi’s talking points.”

“Dean Heller has to go,” fellow activist Patti Jesinoski said. “He’s a RINO, he’s a waterboy, he’s been one since Harry Reid.”

The nation’s most vulnerable Republican senator still has structural and financial advantages with more than 470 days to go before the 2018 election that could fend off an insurgent primary challenger. And floating in the minds of any potential challenger is the fact that Heller has never lost a race since entering Nevada’s political scene in 1990. His campaign declined to answer questions on this story.

The name most often floated as a potential Heller challenger is Danny Tarkanian, the son of legendary UNLV basketball coach Jerry Tarkanian and a perennial Republican candidate who’s beaten better-funded candidates in several primary races. Tarkanian said that his main interest in running for Senate would be to take on Democratic Rep. Jacky Rosen, whom he sued for defamation following his narrow loss to her in the 2016 election.

“I’d like to see how Jacky would run against me without defaming me, and I think I would beat her if we did,” he said.

Tarkanian said it was “more likely at this point that he’d run in the state’s 3rd congressional district, where he lost in 2016 by fewer than 4,000 votes out of more than 300,000 cast. He said no one from President Donald Trump’s campaign had reached out to him about running against Heller, and brushed away suggestions that Heller’s handling of the health care debate would affect his decision.

“You’re not going to run against an incumbent senator based upon one vote that he’s made in his entire career,” he said. “I know it’s hot right now, but in June of next year they’ll be on to someone else. So what he does in this vote is not going to make up my mind.”

State treasurer and likely gubernatorial candidate Dan Schwartz ruled himself out as a challenger to Heller early, saying that in addition to the senator’s fundraising advantage, he polled the race and found Heller to be viewed favorably by about 53 percent of Republican primary voters, and unfavorably by only 17 percent.

“That’s a pretty big hill to climb,” he said.

Any primary challenger will likely face massive fundraising and organizational obstacles, given the Heller team’s early organizing efforts.

Heller reported raising more than $1.4 million in the last three months and has more than $3.5 million in cash on hand, according to the Las Vegas Review-Journal — putting him significantly ahead of likely Democratic opponent Rosen ($400,000 on hand).

And the senator’s team has made more of an effort to reach out and engage with the state’s historically dysfunctional and squabbling state and county parties, lending support to newly elected Clark County Republican Chair Carl Bunce at a fundraiser earlier this week.

Nevada Republican Party Chairman Michael McDonald said that the party was trying to take a page out of former Democratic Sen. Harry Reid’s book, and present more of a unified front for Republicans running for office. He said that Republicans in rural counties (Heller spent the 4th of July weekend in rural parts of the state including Fallon, Baker, Lovelock, Winnemucca, Ely and Elko) had more access to Heller and other elected officials, and generally realized that avoiding intra-party warfare as much as possible was preferable for keeping and holding Republicans in office.

“I think they realize the value of having that, and not having a primary where it’s kind of like a 16 (person), shotgun primary,” he said. “You’re able to move that forward, when you’re able to advance that, that helps us in the general against a strong Democratic opponent.”

Not all Republicans share that view. Republican National Committee member and early Trump backer Diana Orrock said that Heller would have a “tough time” in 2018 especially given rural Nevada’s strong support for the president.

Heller initially attempted to distance himself from Trump from the start of the 2016 campaign, donating the New York billionaire's campaign contributions to charity in 2015 and never outright endorsed the candidate, saying he had “no intentions of voting for him” in June and was “99 percent sure” he’d vote against Trump in July of that year.

Even though Heller has largely supported Trump’s nominees and policy positions during the last 6 months, Orrock said it would be difficult to forget his past opposition.

“It doesn’t help that he’s a U.S. senator who has not been on Trump’s side,” she said. “That just doesn’t bode well for somebody who’s got a Republican president now, and you’re still not on board with the president. I don’t think that’s a very smart tactic.”

A Republican operative with experience running campaigns in Nevada called Heller’s political operation, which recently undertook a 6-day, 17-county tour across the state, “second to none,” and doubted that any serious candidates would jump in the race unless Trump made an active effort to challenge him.

“I can’t see a real legit person who can raise the $2 million bucks unless Trump recruits somebody and helps them raise money,” he said, putting odds at Trump getting involved at around 10 percent.

Despite reports that major donors including casino executives Sheldon Adelson and Steve Wynn had complained to Heller over his initial opposition to the health care bill, party officials such as Assembly Republican Leader Paul Anderson say that it’s unlikely that unhappiness would lead to them supporting another candidate.

“Privately I’m sure they want him to support the party and support the bill. Publicly they can stomp their feet, do whatever they want, but I just don’t see them throwing a lot of money against him unless he just really goes off the rails and isn’t able to, you know, articulate his position very well,” he said. “But I don’t see that happening. Senator Heller’s a smart guy.”

Despite daily doom-and-gloom dispatches from progressive and Democratic groups, Heller’s reputation isn’t tanked in the state — a July Morning Consult poll found Heller with a 41 percent favorable to 33 percent unfavorable approval rating, with more than a quarter of surveyed voters undecided or without an opinion. Other polls, including one taken by The Nevada Independent in January, indicate that voters see Heller in a much less favorable light.

Taking out an incumbent senator in Nevada would be historical rarity — no sitting senator has been taken out in a primary since the mid 1940s, when Berkeley Bunker defeated appointed Sen. Edward Carville in the continuous 1946 Democratic primary. Bunker, a former appointed senator himself who lost in a primary to then-Gov. James Scrugham in 1942, lost the general election to Republican George Malone.

Anderson said it was very likely that Heller wouldn’t get a “free ride” and would probably attract some primary opponents, but said the challenges were likely too high for any potential “valid” opponents.

“It’s difficult to run a statewide race,” he said. “It’s very costly, as you know, and coming up against an incumbent in a race that very well may be one of the most difficult races to win for a general election this cycle. I would say that that may scare some folks off.”

But despite renewed efforts to build intra-party support and a financial head start, many Republicans still aren’t thrilled with the likely party nominee.

“As Republicans, we’re supposed to support Donald Trump, we’re supposed to support repeal (of the ACA), and we’re supposed to support Dean Heller,” newly elected Clark County Republican Party Chair Carl Bunce said. “Somewhere in that triangle, it’s tough to be a Republican.”

Michelle Rindels contributed to this story.