Retired Phoenix police Officer Paul Penzone is challenging incumbent Joe Arpaio in the race for Maricopa County sheriff.
The announcement Wednesday marks Penzone's second attempt to unseat Arpaio.
He lost the 2012 sheriff's race by 6 percentage points in what was the second closest election in Arpaio's 23 years in office.
Penzone joins William Hall and former corrections Officer Joe Rodriguez in the race's Democratic field.
“Judge the Sheriff how you choose to, but I will put people first safety first,” said Penzone. "I will not tolerate abuse or unprofessionalism or lack of integrity.”
“We need to raise enough money that I can get my message out there and not to expect to be dollar for dollar with Sheriff Arpaio,” Penzone said.
Arpaio campaign issued the following statement Wednesday:
"The voters of Maricopa County rejected Paul Penzone once before and they'll do it again. Right out of the gate, Penzone has chosen to level petty, personal attacks against Sheriff Joe Arpaio. This is not what voters expect out of a campaign for the top law enforcement position in the county. In short, Paul Penzone lacks the character and experience necessary to be Sheriff."
Arpaio's GOP challengers are former Buckeye Police Chief Dan Saban, Roger Baldwin, Mike Bodak and Marsha Hill.
Saban ran unsuccessfully against Arpaio in 2004 and 2008.
Independent Kenneth Baker also is running.
Arpaio spent $8.2 million during the 2012 race, nearly 14 times as much as Penzone.
Penzone says he won't focus on Arpaio's vulnerabilities and instead will promote his commitment to law enforcement.