Associated Press

Liberal hedge fund tycoon George Soros has contributed $300,000 to a political group opposing Sheriff Joe Arpaio’s bid for a seventh term in office, according to a campaign finance report filed Thursday that confirms the billionaire’s involvement in the race.

Soros was the sole contributor listed in the first report filed by Maricopa Strong, which has sent several mailers across the county in recent weeks that were critical of Arpaio.

MORE: Roberts: Arpaio in for a rough October |Penzone sues for defamation over TV ad | Arpaio raises nearly $10M for tough re-election campaign

One of the group’s fliers promoted Democratic challenger Paul Penzone, who brought in $188,000 over the last month, compared with $725,000 raised by Arpaio.

A recent fundraising email by Arpaio to his backers focused heavily on Soros’ involvement in the race.

Over the last year, Soros has contributed $3.9 million to Democrats in district attorney races in Chicago, St. Louis, Orlando, Houston, Albuquerque, Lowndes County in Mississippi and Caddo Parish in Louisiana.

Of the seven district attorney candidates that Soros-linked groups have backed, two have already been elected and four won primaries. Only one lost.

In all, Arpaio has raised $12 million over the course of the campaign and has $1.2 million in cash on hand.

Penzone has collected $400,000 in total contributions and has $188,000 in cash left.

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