Controversial former Arizona county Sheriff Joe Arpaio announced Tuesday that he will run for Senate, a decision that casts further uncertainty into the state's GOP Senate primary.

Arpaio gained popularity among immigration hardliners during his time as Maricopa County sheriff, representing the Phoenix area, proudly calling himself "America's toughest sheriff" and touting a strict approach to border security.

Some of his tactics opened him up to criticisms and allegations of racial profiling and mistreating prisoners. President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE pardoned Arpaio last year after he was convicted of ignoring a court order related to racial profiling in his division.

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The sheriff, who lost his elected sheriff's office last year after more than two decades has long floated bids for higher office. But he announced on Twitter he would run for Senate “to support the agenda and policies of President Donald Trump.” If he wins the seat, Arpaio would be 86-years-old by the time he took office.

The statement came shortly after the publication of an interview with Washington Examiner, where Arpaio explained his reasoning for running to replace retiring Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeRepublican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style Bush endorsing Biden? Don't hold your breath MORE (R-Ariz.).

“I have a lot to offer. I’m a big supporter of President Trump,” he told the paper.

“I’m going to have to work hard; you don’t take anything for granted. But I would not being doing this if I thought that I could not win. I’m not here to get my name in the paper, I get that every day, anyway,” he said.

Arpaio has not yet filed an official statement of candidacy with the Federal Election Commission — he has two weeks to do so by law. Arpaio has flirted with bids for higher office before, only to not run. But his campaign website tells supporters that he is running, and has already begun accepting campaign cash under the laws for Senate candidates

Arpaio’s announcement will be met by trepidation among establishment Republicans who have asserted after last month’s defeat in Alabama, where the party rallied around a candidate accused of sexual molestation of a teenage girl, that Republicans should not nominate controversial candidates.

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Arpaio’s many controversial actions as sheriff included the use of an outdoor jail where he housed inmates in tents in the Arizona heat. A previous version of the sheriff’s office website touted that fact, noting that “all inmates ... are subjected to the elements.”

He also played a major role in the movement questioning former President Obama’s birthplace, a conspiracy theory that Trump himself furthered until deep into his presidential bid.

He found himself in legal trouble last year after he violated a federal order related to a racial profiling case against him. But Trump pardoned Arpaio before he could face sentencing in a move that drew criticism from Republicans and Democrats alike.

Arpaio’s entry into the race complicates the calculus for former state Sen. Kelli Ward, who had been the only major candidate in the Republican primary.

Ward has been endorsed by former White House chief strategist Stephen Bannon. But her campaign took a hit last week when Bannon landed on the wrong side of a dramatic rebuke from Trump after a new book quoted Bannon disparaging Trump’s son as “unpatriotic” for taking a meeting with a Russian lawyer during the campaign.

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Now that her top backer has lost influence within the GOP, Ward faces the prospect of a crowded anti-establishment lane.

The Republican establishment had already proven wary of Ward. The Senate Leadership Fund, the super PAC aligned with Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE (R-Ky.), has repeatedly criticized her candidacy in the past. The group did not comment on Arpaio’s entrance.

Republican Rep. Martha McSally Martha Elizabeth McSallySenate Republicans face tough decision on replacing Ginsburg Democratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy What Senate Republicans have said about election-year Supreme Court vacancies MORE (R-Ariz.) is also expected to jump in soon but has not made a formal announcement. She could stand to benefit from Ward and Arpaio’s similar constituencies if the candidates split each other’s votes.

But Arpaio would also be an opponent with strong name identification and the unofficial imprimatur of Trump through his pardon.

The winner of the GOP primary will likely face Rep. Kyrsten Sinema (D-Ariz.), who is the heavy favorite in the Democratic primary.

Trump won the state by 4 points in 2016 despite a quixotic push by Democrats to win Arizona. While Democrats are emboldened by Trump’s low approval ratings and a significant Democratic lead on the generic ballot, Arizona has not elected a Democratic senator since 1988.