If Arpaio follows through and files his candidacy papers, the race could feature one of President Trump's most vocal supporters trying to replace one of his fiercest detractors.
Trump did claim to have done the nation a great service by raising the profile of the issue and prompting Obama to release a document he said was a long-form birth certificate from Hawaii.
He will not support Arpaio if he becomes the GOP nominee, he said in the interview.
Arpaio endorsed Trump in 2016 and appeared alongside him at campaign appearances, including a large outdoor event in the lawman's hometown of Fountain Hills, outside Phoenix.
If Mr Arpaio gets Mr Trump's endorsement, it could win him the Republican nomination. Gallego, not surprisingly, graduated from Harvard University, is a member of the Congressional Progressive Caucus, and sports a treasonous Freedom Index rating of just 16 out of 100. The media is going to say every nasty thing they can think of and try to break me.
In an interview with the Washington Examiner published Tuesday, the 85-year-old Arpaio said he intended to run for the seat Sen.
Translation: Enforcing the law under SB 1070 would be inconvenient for federal immigration authorities and so must be blocked.
"We pumped a lot of money into these foreign countries - tons of money to help their security, law enforcement, and that's OK, but you have to do it right".
On the one hand, he will draw unwanted attention for the GOP nationally. I have a friend here who grew up down the street from me, who's also from Maricopa County, texted me yesterday 'Can you believe this blank with Joe Arpaio?' He spent almost a quarter-century in that office. Last year he was convicted of contempt of court for wilfully defying court orders to stop.
Arpaio responded to Flake's criticism, calling him out on his decision not to run again.
"And we have the evidence", the sheriff said. While Arpaio's efforts to prove Obama wrong never came true, he was found guilty of racial profiling and lost his re-election bid to a Democrat. So when Mr Arpaio began touting himself as a possible contender for the US Senate seat that Jeff Flake is vacating, many Arizonans assumed he was seeking nothing more than publicity.
Trump won the state by 4 points in 2016. But since Flake announced his retirement, McSally has taken a different approach towards the president.
Former Arizona legislator Kelli Ward entered the race months ago. Arpaio's meticulously cultivated tough guy image apparently didn't extend to harsh treatment for sex criminals who targeted women and children.
It wasn't the doctor from Milan heading to America.