Republican Joe Arpaio, a close ally of President Trump and former sheriff known for his provocative approach to combatting illegal immigration, is running for Senate in Arizona.

The 85-year-old Arpaio could shake up the late August Republican primary in a critical open-seat race to replace retiring Sen. Jeff Flake, R-Ariz. Trump pardoned Arpaio last summer, sparing the former sheriff jail time after he was convicted of ignoring a federal court order in a racial-profiling case.

The polarizing yet iconic former Maricopa County sheriff, beloved by many conservatives for his hawkish immigration policies, presents an alternative to the unimpressive Kelli Ward and a potential obstacle to Rep. Martha McSally. She is expected to launch within days and is widely viewed as the Republicans’ strongest general election candidate.