President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE's decision to remain on the sidelines has caused a protracted and costly Republican primary fight in Arizona, where the three candidates are heavily playing up their Trump bona fides despite no endorsement in sight.

All three candidates – establishment favorite Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R-Ariz.), her main GOP rival Kelli Ward, and outside shot former Maricopa County Sheriff Joe Arpaio – have personal connections to Trump, a reason political observers believe have led him to sit this primary out.

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But the absence of a decisive endorsement has each candidate and their financial backers believing they can still win the Aug. 28 primary, leading to more than $7 million being spent in the race by outside groups alone.

Those kind of numbers and the intensity of the fight are worrying some Republicans as McSally, the candidate who is leading in the polls and the one believed to have the most general election appeal, is too mired in a primary fight to be focused on likely Democratic opponent, Rep. Kyrsten Sinema (D-Ariz.).

The race for the seat being vacated by departing Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R-Ariz.) is critical for Republican hopes to retain its narrow 1-seat majority in the Senate. It is currently seen as a "toss-up" by The Cook Political Report, in a state where Democrats haven’t won a Senate race since 1988, and that Trump won by less than 4 points in 2016.

“McSally has been spending precious treasure ... against Ward, and is still trying to put Ward to bed,” said a Arizona Republican consultant, who requested anonymity to speak candidly about the race with The Hill. “It’s problematic that she’s not focusing on Sinema.”

Trump’s absence from the primary is notable since he’s been weighing in more contested GOP primaries this year.

An endorsement has been its weight in gold in many instances, given Trump's popularity among Republicans, propelling once outside-shot candidates such as Brian Kemp and Kris Kobach to victories in Republican gubernatorial primaries in Georgia and Kansas, respectively.

Trump is believed to like McSally, who has worked closely with Trump while in Congress and who has visited the Oval Office several times. Her campaign, for example, has touted Trump’s praise at a recent defense bill signing where he called McSally “terrific.”

National Republicans believe McSally is their best shot at the Senate seat, seeing Ward as too extreme for the state's large base of independent voters.

While the National Republican Senatorial Committee (NRSC) hasn’t publicly weighed in on the race, Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellTrump 'no longer angry' at Romney because of Supreme Court stance On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline The Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power MORE (R-Ky.) has lauded her as one of the party’s top recruits this cycle.

And the NRSC reportedly asked Trump to endorse McSally ahead of the primary, according to Politico. The problem is that the president has also praised Ward, while pardoning Arpaio following his conviction for criminal contempt.

“I think [Trump] has a personal affinity to Martha, I think he sees her as tough and willing to speak her mind,” said Sean Noble, a longtime Arizona Republican strategist. “I think whether he does or not, she’s going to win. If he weighs in, she probably wins by larger margin.”

The absence of an endorsement is leading to a surge in spending in support of the two main Republican candidates.

Outside groups have already spent more than $7 million. The biggest spender has been Defend Arizona, a super PAC backing McSally, which has spent about $3.8 million and is currently up on the air with ads attacking Ward – and pushing back on anti-McSally ads from Democratic groups.

McSally has been up on the airwaves going hard against Ward, a former state senator, and painting her as someone who doesn’t support Trump and his immigration agenda. McSally also tagged her as a former Democrat, since Ward was registered as one when she was 18.

Meanwhile, Ward is running to the right of McSally and is frequently attacking McSally as being anti-Trump since McSally still hasn’t said whether she voted for Trump in the 2016 election. And Ward has also called out McSally for being too soft on immigration and border security, dubbing her “McAmnesty.”

Ward is also seeking to tie herself to Trump, sending a mailer with a Trump tweet praising Ward for running.

But the tweet, which was from August 2017, was shortened and the context was misleading since it was actually tweeted when she was running against Flake, a strong Trump critic who ultimately decided not to seek re-election because he believed he would not survive a Republican primary.

Ward has stood by those mailers, arguing in a Fox News interview on Friday that the tweet still applies because she sees McSally as “Jeff Flake 2.0.”

Outside groups are also spending heavily on Ward's behalf. GOP mega-donors Robert Mercer and Andrew Beals have contributed collectively more than a $1 million to super PAC KelliPAC, which is seeking to boost Ward.

The bitterness of the attacks could be taking a toll. McSally has consistently led primary polls for months, and the latest public polling has the congresswoman up 20 points, according to Phoenix-based OH Predictive Insights.

But Republicans who spoke to The Hill say they’ve seen numbers that are much closer and within single digits, raising the potential of an upset. Ward has contended that internal polls show her ahead.

Republicans are also worried because Arizona's late August primary means that McSally – should she emerge as the winner – would have an an abbreviated general election period compared to most other competitive Senate states whose primaries wrapped up weeks or even months ago.

Meanwhile, Sinema will not be facing a competitive primary and has already spent millions of dollars on TV ads where she’s been able to define herself as an independent, with no GOP pushback.

Both McSally and Sinema have been prolific fundraisers. McSally raised $6.6 million since the beginning of the year and has spent $2.4 million. But Sinema has brought in $9.5 million since January 2017 and has $5.3 million on hand.

Ward has languished in fundraising compared to both of them, raising $2.6 million since January 2017 and has about $363,000 in the bank.

Democratic groups have already gotten a head start attacking McSally before the primary wraps up. Priorities USA, a major Democratic super PAC, has spent a total of more than $600,000 on ads targeting McSally.

Red and Gold, a Democratic group that will disclose its donors after the August primary, has funneled in $1.6 million hammering away at McSally.

Also worryingly for Republicans, most polls show Sinema leading in head-to-head matchups against all three Republicans.

Republicans are hopeful that the gap in the polls will close once there’s an official GOP nominee. And while Democrats are enjoying a spike in enthusiasm around the country, Republicans argue that they’ll still dominate turnout.

But they believe their prospects of winning are not being helped at a time when Sinema has had plenty of time to define herself as a moderate bipartisan candidate with independent voters.

“Sinema has been able to define herself as a moderate, middle-of-the-road bipartisan type of candidate,” said Wes Gullett, a GOP strategist in Arizona. “When you come after and call her a liberal, is it going to stick because she’s had so much time to define herself?”