THROUGHOUT his 24-year tenure as the sheriff of Maricopa County, Arizona, Joe Arpaio repeatedly suggested that he would run for higher office, usually the governorship. But “America’s toughest sheriff,” as he called himself, never did. 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.

On January 9, Mr Arpaio announced that he would run, “for the good of our country”. The former sheriff, famous for using his department to enforce immigration laws, housing prisoners in tents and dressing them in pink underwear, said his intention was to support Donald Trump’s agenda in the Senate. 

Many had assumed the 85-year-old’s career was over. The tough-on-crime policies that for years endeared Mr Arpaio to voters in Maricopa County, home to more than 4m people—about 60% of Arizona’s population—resulted in millions of dollars in legal settlements. In 2013 a federal judge found that his department had used race and ethnicity as grounds for pulling over local residents, in pursuit of immigrants without legal status. Last year he was convicted of contempt of court for wilfully defying court orders to stop. In 2016, after re-electing Mr Arpaio six times, voters in the reliably Republican county decided they’d had enough and opted instead for his Democratic opponent. 

Mr Arpaio’s announcement is likely to widen the field for Arizona’s Senate race further. In October, Mr Flake’s announcement that he would not seek re-election left Kelli Ward, a conservative former state senator regarded by many as a fringe candidate, as the only contender for the seat. Since then, many Republicans, especially those on the party’s establishment wing, have pinned their hopes on Martha McSally, a congresswoman from Tucson, the state’s second largest city, who was the first female fighter pilot to fly a combat mission and command a fighter squadron. In November, she told colleagues in that she would run for Mr Flake’s seat. She appears poised to formally enter the race soon. 

With her compelling personal story and high-powered fundraising record, most observers had expected Ms McSally to easily dispatch Mrs Ward in the Republican primary. How will Mr Arpaio’s unexpected candidacy change the equation? Despite his obvious faults and his defeat in 2016, the former sheriff still commands the loyalty of many voters and has a proven ability to raise millions of dollars from supporters across the nation.

But Mr Arpaio’s record as a demagogic, law-breaking attention-seeker could allow Ms McSally to cast herself as the only candidate who is capable of winning the general election. And Ms McSally, who is distrusted by many in the Republican Party’s grassroots conservative wing, may benefit from having Mr Arpaio and Mrs Ward compete for the same base of voters. If, however, the primary is a head-to-head race between Mr Arpaio and Ms McSally, the race is likely to be tighter.  

If Mr Arpaio gets Mr Trump’s endorsement, it could win him the Republican nomination. Mr Arpaio is popular among the president’s base and shares many of his hardline views on illegal immigration. Mr Trump, who pardoned Mr Arpaio for his contempt of court conviction last year, has lavished praise on him. But his endorsement may not be automatic. The president has also publicly praised Ms McSally—and Mrs Ward as well—calling the congresswoman, who has consistently voted with his agenda, “my friend” and “the real deal.” 

Whichever Republican makes it to the general election will almost certainly face Congresswoman Kyrsten Sinema, a fundraising dynamo with a strong centrist record. She stands a strong chance of becoming the first Democrat elected to the Senate from traditionally Republican Arizona since 1988. The presence of a top-tier Democratic candidate, in a year that is widely expected to favour her party, raises the stakes for a Senate race that in many other years would be all but decided in the primary.