The spending is part of the billionaire's nationwide push on criminal justice and immigration reform.

George Soros has contributed $2 million to a group working to defeat Maricopa County Sheriff Joe Arpaio in Arizona, the latest target of Soros' big spending in local law enforcement campaigns over the past year.

The Soros-funded PAC, Maricopa Strong, will file campaign finance documents Friday showing Soros' multimillion dollar investment against Arpaio, along with $500,000 from Texas energy billionaires Laura and John Arnold and $250,000 from Laurene Powell Jobs (widow of Apple co-founder Steve Jobs). The group had previously reported a $300,000 donation from Soros, one of the Democratic Party's biggest donors.

Soros has spent millions in 2015 and 2016 funding campaigns to defeat local prosecutors around the country and elect new ones who back criminal justice reform measures. Soros-backed groups are currently spending big in three big-city district attorney races: Houston's Harris County, where Soros has contributed over $1 million, according to local campaign finance filings; Gilpin and Jefferson counties outside Denver, where Soros has given about $1.5 million to unseat an incumbent; and Phoenix's Maricopa County, where a Soros-funded PAC has also spent over $1 million against the Republican district attorney, Bill Montgomery.

But Soros' spending against Arpaio, a high-profile liberal boogeyman, is his single biggest investment in a local race this year, as well as the billionaire's first effort against a sheriff. It folds in immigration reform, another policy passion of Soros', alongside criminal justice reform.

Arpaio made his name in Arizona and nationally as an opponent of illegal immigration. He was charged by federal prosecutors last month with contempt of court for violating an order to halt discriminatory policing practices.

Maricopa Strong has spent $2.9 million in the sheriff's race, with the donations from Soros and others funding a flurry of mailers and TV ads boosting Democratic candidate Paul Penzone and hammering Arpaio. Soros has typically been the sole funder of his local outside-spending campaigns around the country, though Jobs and the Arnolds joined him in funding Maricopa Strong.

"Rapes, assaults, even child molestation remained uninvestigated while Arpaio focuses on his personal agenda," the narrator says in one of the group's TV ads. "Arpaio talks tough, but he doesn't keep us safe."