Rep. Jeff Flake hasn’t made many friends during nearly a dozen years in Congress, possibly hampering his ability to shut down an unexpectedly tough primary opponent in his bid for Arizona’s Republican nomination for Senate.

Flake’s limited-government approach and stubborn resistance to earmarks have long put him at odds with K Street, leaving him with less financial support from Washington, D.C., lobbyists than would otherwise be expected of a sitting Member running for a winnable open Senate seat. But Flake appears equally detached from his colleagues in Arizona’s Republican Congressional delegation, none of whom have expressed public enthusiasm about his Senate bid that is now threatened by Wil Cardon, a wealthy GOP businessman dumping large sums of his personal fortune into the primary.

Flake does have the broad support of Washington’s tea party community, including groups such as the Club for Growth and Members such as Sen. Jim DeMint (S.C.) and House Budget Chairman Paul Ryan (Wis.). And Sen. John McCain has quietly headlined at least three fundraisers for the six-term Congressman since last summer. But among Arizona Republicans serving on Capitol Hill, Flake’s relationships are thin, with his libertarian approach to issues such as illegal immigration — he is not a hardliner — generating some ideological tension. A GOP operative with Arizona ties said Flake’s differences of opinion with Grand Canyon State Republicans on some key issues could explain why none had endorsed his Senate bid as of Wednesday.

Particularly because some of these Members are running in competitive House primaries of their own, backing Flake carries risks at home. “There are a decent amount of grass-roots conservative activists who don’t have the same view of Flake as people in Washington do,” a Congressional political operative said. “That’s the political reality. … It comes down to, ‘Do you want to take that flak?’”

After a rough couple of months for Flake’s Senate campaign, his prospects appear to be improving as the Aug. 28 primary comes into view. If Flake is nominated, he and former Surgeon General Richard Carmona (D) will battle in the fall for the right to succeed retiring Senate Minority Whip Jon Kyl (R).  

Cardon continues to pummel Flake relentlessly on television, with the Congressman’s opponents on both sides of the aisle dumping opposition research to fuel a barrage of negative news stories. In fact, Flake has been vastly outspent, forcing him to burn through more resources in the primary than originally planned. So far, his delegation colleagues have yet to race to the Congressman’s rescue.

That could change, however. McCain said in an interview this week that he planned to endorse Flake, although he gave no hint on the timing. “Stand by,” Arizona’s senior Senator told Roll Call.  

Kyl, who is closely aligned with Arizona conservatives, is more difficult to read.

Sources throughout Arizona stress that he and Flake have a strong relationship and he is expected to endorse soon. But Kyl has done little compared with last cycle, when he moved early to help McCain repair his relationships with conservative activists and publicly helped the 2008 GOP presidential nominee defeat former Rep. J.D. Hayworth in a 2010 primary that many thought could go the other way.  

This cycle, Kyl has endorsed in at least one competitive Arizona GOP primary. He backed Rep. Ben Quayle, who was redistricted into a race against Rep. David Schweikert. “Stay tuned,” a noncommittal Kyl said when asked whether he planned to endorse in the Senate primary.

For now, Rep. Trent Franks is the only Arizona Republican in Congress to endorse, and he is backing Cardon. That development surprised few in the state. Even though Franks told Roll Call on Monday that he loves and respects both candidates, he and Flake are known rivals. Additionally, Franks was on the verge of joining Flake in the Senate race, pulling the plug on his bid at the last minute.

“Probably the hardest thing anybody does in these kinds of races is to make a distinctive choice in a primary,” Franks said. He cited an old friendship with Cardon and Cardon’s “full spectrum” conservatism as his reasons for endorsing.

Flake’s colleagues who have declined to endorse could have self-serving concerns unrelated to his lack of close personal relationships with fellow state Republicans.

Quayle and Schweikert are engaged in a rough Member-vs.-Member race, while Rep. Paul Gosar faces a fierce primary opponent in state Sen. Ron Gould. The result is a mad scramble for resources and support and a reluctance to alienate anyone within the state party by picking sides in a Senate race.

“I don’t know,” Quayle said when asked about the lack of endorsements. “My focus right now is just on my race. I know Jeff. I like Jeff a lot. He’s been a real fiscal hawk, and the main point is we need to make sure a Republican holds onto that seat.”

Still, there is sense among Arizona Republicans that Flake still has the upper hand and will ultimately win the nomination.

Over the weekend, the Arizona Republic published a lengthy story raising questions about Cardon’s record as an employer of undocumented workers. The Flake campaign pounced, immediately rolling out a negative television ad on the issue.

Flake’s troubles and the negative nature of the primary campaign have raised Democratic hopes for the seat.

Democrats predicted that Flake will win the nomination but emerge from the late August primary bloodied and broke, without enough time to replenish his coffers. Republican strategists are split. Some dismiss the Democratic argument on the grounds that President Barack Obama’s unpopularity in Arizona will drag down the rest of the ticket. Others are worried Flake could be a damaged nominee.

“I think the real impact is going to be in the general,” said an unaffiliated GOP strategist in the concerned camp.

Humberto Sanchez contributed to this report.