Arpaio, a polarizing figure who gained notoriety for racially profiling Latinos, contradicted his own words from a day earlier.
Arpaio's announcement is likely to have the biggest impact on Kelli Ward, another Tea Party GOP extremist planning to run for the party nomination.
FOX 10's John Hook talked to Arpaio about his decision to run.
"I think he would just suck up most of her support".
"And anytime you want to come down, or anybody we'll be glad to show you the evidence", he added.
Former Arizona sheriff Joe Arpaio, who was recently criminally convicted and pardoned by President Donald Trump, told NPR that young unauthorized immigrants should be deported. He also said the president had not asked him to run for the Senate.
"So no, it had nothing to do with it. I don't care if I lose elections or anything", he said during a sitdown with WABC Radio's Rita Cosby and Curtis Sliwa.
The former sheriff was also asked if this run is more about his ego - that he's missed being in the spotlight. "At least I got the guts to face all the detractors - Democratic Party, you name it". "If you were in the Senate, would you do that as well?" Let's see how long they remember Flake, how long they remember governors, they all leave. Come on. Everybody knows me in this country anyway. He flirted with running for governor no fewer than five times over the years before abandoning the idea. This isn't a stunt.
Until now, Ward was considered to be the Republican front-runner. Sinema announced back in September that she would run for the Senate seat.
Attorney and community activist Deedra Abboud made headlines when she received hateful attacks on her Facebook page for being Muslim back in July.
"I started this because of fake documents, government documents", Arpaio explained again. That's why Arizona voters kicked him out of office in November.
Joe Arpaio speaks at his office on January 10, 2018.
Gallego opposes SB 1070, Arizona's attempt to enhance its protection against the flood of illegal immigrants entering the state.
The Senate candidate further said that he wouldn't close the US border to all immigrants, but indicated that he wanted "the right people to come into our country". Nevertheless, Trump and Arpaio continued to loudly express doubts about its authenticity.
McSally hasn't officially declared yet and at one point, Ward was the only one running. When they can't get you on one thing, they always throw the race card. Arpaio said in an interview with The Associated Press on Wednesday.
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