Maricopa County Sheriff Joe Arpaio and Mesa lawmaker Russell Pearce have put aside years of political fighting to forge an unlikely and uneasy alliance.

Arpaio has agreed to be a guest of honor at an upcoming political fundraiser for Pearce, who is considering a run against Rep. Jeff Flake, R-Ariz., in next year’s primary.

Pearce, a Republican who has been critical of Flake’s position on illegal immigration, has promised to make securing the border a hallmark of his potential campaign.

“Shame on folks who can’t set aside their differences when there are big issues like immigration on the table,” said Pearce. “The No. 1 issue is immigration and he (Arpaio) has been out in front of that.”

The self-described “toughest sheriff in the county” said he’s backing Pearce next year because of Pearce’s long-standing fight to curb illegal immigration and because Congress needs a tougher voice on the issue.

For example, Arpaio supported Pearce’s efforts to secure $1.4 million from the Legislature to enforce the state’s human-smuggling law as well as his efforts to pass an employer-sanctions bill last year that aims to punish businesses that knowingly hire illegal immigrants.

But the newly formed partnership of the longtime rivals could be an edgy and nervous union as friction remains.

The bad blood dates back to 1993 when Pearce agreed to serve as chief deputy for the newly elected Arpaio. But after one year, Pearce left the office, saying the sheriff was preparing to break a campaign promise and run for re-election.

Initially, Arpaio had run on a campaign platform that included saying the sheriff’s office should be an appointed position and not an elected office. That was a stance that Pearce strongly disagreed with, and one on which Arpaio later changed his mind.

“I learned real quickly how important it is that this is an elected office,” Arpaio said. “I made a mistake.”

Regardless, Arpaio disagrees that differences over the office led to the breakup but would not say exactly why the partnership didn’t work.

“Let’s just say that I’m my own man and that’s the way it goes,” Arpaio said.

Once Pearce left, Arpaio said he made a personal phone call to then-Gov. Fife Symington and asked the state’s top executive to appoint Pearce as Director of the Governors Office of Highway Safety — which Symington did.

Besides political differences, there also has been a long-standing dispute over who should take credit for one of Arpaio’s most recognizable endeavors — the Tent City jail.

Pearce has said it was his idea originally to put up military-style tents to house inmates, but he has allowed the sheriff to take credit for it.

The sheriff sees it very differently.

“Look, it was in my campaign literature at the time,” Arpaio said. “Sure, I don’t come up with all the ideas, I do delegate responsibility. But I’m the sheriff and nothing gets done without my approval.”

While those incidents are in the distant past, tensions between Arpaio and Pearce’s family escalated recently over an incident involving Arpaio and Pearce’s son, Sean Pearce, a deputy shot in the line of duty in 2004.

Sean Pearce was highly critical of the recent shakeup in the sheriff’s SWAT unit that was seen as rewarding Arpaio’s political allies. It also was reported Russell Pearce’s wife refused to shake hands with the sheriff at the hospital where Sean Pearce was taken after being shot.

“That wasn’t between us,” Arpaio said. “And they certainly have a right to their own opinion.”

Regardless, Arpaio’s backing gives Pearce a powerful political ally in a race where illegal immigration promises to be one of the key issues.

Political pollster Earl de Berg, with Behavior Research Center, said the sheriff would bring out a lot of loyal voters, but it’s not clear how much that will actually help Pearce.

“I’m just not convinced that he (Arpaio) will bring a lot of new voters to Pearce that he doesn’t have already,” he said.