PHOENIX — Arizona Republican Party Chairman Robert Graham says the “mudslinging” in the GOP gubernatorial fray has gotten so bad he had to tell contenders to cool it, or risk electing Democrat Fred DuVal in November.

In a letter this past week to candidates, Graham told them he is receiving “an increasing volume of phone calls, emails and physical letters voicing Republican voter disappointment with the level of negative campaigning.”

Graham said Republicans “expect an aggressive and vibrant exchange of ideas” on issues. And he said voters anticipate there will be “tension between candidates” during a campaign.

“But their feedback regarding the personal attacks is an overwhelming disappointment,” he told the six contenders.

Graham said this isn’t just an idle worry about tarnishing the GOP brand.

He said one of them will become the party standard-bearer for the Nov. 4 general election, and the attacks that are occurring will have an effect long after the Aug. 26 primary.

“I worry our nominee will have such high unfavorability ratings that we will have a tough time winning, even with many favorable headwinds,” Graham wrote.

When asked about the letter, Graham said there was no one single event that caused him to send it.

The battle for governor has not just been pitched, but oftentimes negative, particularly among the front-runners.

Scott Smith and Christine Jones have targeted what has been characterized as Doug Ducey’s lackluster performance as chief executive of Cold Stone Creamery before he sold it.

Ducey has responded in kind, questioning Smith’s own business record as a homebuilder. And he has said the job Jones held at GoDaddy was that of a “line employee ... with no leadership experience.”

Meanwhile, Andrew Thomas, who is trailing the field in polls, has attacked everyone else in the race, calling Frank Riggs a “carpetbagger,” Jones a “committed feminist,” and said Ken Bennett “buckled to pressure from media elites” because he stopped helping Maricopa County Sheriff Joe Arpaio with his investigation into President Obama’s birth certificate.

And he said all five of his foes “supported the gay-rights agenda” because they all urged Gov. Jan Brewer to veto SB 1062, which would have expanded the ability of private businesses to discriminate based on owners’ religious beliefs.

“We’re right in that heated spot where emotions are at the pinnacle,” said Graham, who has seen the mailers and the TV commercials. The letter, he said, is his effort to deal with all that.

“The idea was just to kind of call it out right now,” he said.

He said, though, that it is up to each candidate to determine exactly what is fair game, and when accusations cross the line and become counterproductive — at least for the party and its brand.

Graham said he is trying to sell the idea that voters “want to hear messages that are relevant” to the things that affect them.

“And so, a lot of times when people start slinging mud, it’s not relevant,” he said.

Graham conceded that he has one big obstacle working against his message: Going negative in a campaign seems to work.

“As much as I suggest, campaigns are going to do what they believe is in the best interests of their candidate’s race,” he said. “But we’re trying to get them to do it in a way that demonstrates style and legitimizes the whole process for all the other voters.”

Ducey spokeswoman Melissa DeLaney said her candidate wants to focus on the issues, and will respect Graham’s request “as long as our opponents do the same.”

But Jones is unlikely to back off.

Spokeswoman Anna Haberlein said Ducey is campaigning “on his record at Cold Stone.” Haberlein said Jones wants Ducey to be “transparent and honest about that record.”

And Smith, in a letter to Graham, said he has no problem sticking to the issues. But he said the chairman needs to make the same request to “outside supporters” who have been doing commercials, mailers and “push” polls.

The dialogue in the race has been at least partly hijacked by outsiders with their own committees that are not responsive to, and legally cannot coordinate with, the candidates themselves. And they’re spending a lot.

Better Leaders for Arizona has spent nearly $1 million attacking Ducey and more than $225,000 in support of Jones. Meanwhile, Concerned Leaders for Arizona has spent close to $220,000 to elect Ducey, with more than $34,000 in efforts against Jones and another nearly $60,000 attacking Smith.

Then there’s the 60 Plus Association, which has put more than $330,000 into efforts against Jones and another more than $280,000 going after Smith.

And none of that takes into account the commercials being run by Veterans for a Strong America, which insists it not only doesn’t have to disclose its donors, but also is exempt from reporting its spending on its attacks on Jones.