Joe Arpaio, the longtime Phoenix-area sheriff whose headline-grabbing approach to immigration made him an ally of President Trump, will run in the 2018 Republican primary to replace Sen. Jeff Flake (R-Ariz.).

Arpaio, 85, made the bid official in an interview with the Washington Examiner.

Arpaio, who has frequently talked about seeking higher office, said he decided to run as a "big supporter of President Trump" who would back the president wholeheartedly. He is entering a primary against Kelli Ward, a former state senator also running as a Trump ally; his decision may create an opening for Rep. Martha McSally (R-Ariz.), a Republican with more moderate views on immigration who is contemplating a bid for the seat and is backed by party leaders in Washington.

"Sheriff Joe has been a patriot, but at the end of the day in terms of running for this election Kelli Ward is going to be hard to beat," said Eric Beach, a political strategist for Ward's campaign. "I'm confident that this will not split the vote. The reality is that Kelly has a lot of momentum in the race."