Billionaire and frequent liberal donor George Soros gave $6 million to the leading super PAC backing Democratic candidate Hillary Clinton in December. According to a report filed with the Federal Election Commission, the group, Priorities USA Action, brought in more than $25 million in the latter half of 2015.

Soros’ contributions to Priorities during this election cycle total $7 million, and his most recent donation makes up nearly a quarter of its fundraising in the last six months.

view photo essay Photos from the Iowa campaign trail As Iowans prepare to cast the first votes of the 2016 presidential election, Democrat and Republican candidates have been blanketing the state.

Other major donations to the super PAC last year included $5 million from media mogul Haim Saban and his wife Cheryl, $2.3 million from philanthropist Laure Woods, and $2.5 million from financier Donald Sussman.

Emails from Clinton’s private server released by the State Department show that Soros regretted backing then-candidate Barack Obama during the 2008 Democratic primaries. In an email to Clinton in 2012, a friend reported that Soros “said he’s been impressed that he can always call/meet with you on an issue of policy and said he hasn’t met with the President ever … He then said he regretted his decision in the primary – he likes to admit mistakes when he makes them and that was one of them. He then extolled his work with you from your time as First Lady on.”

In 2004, Soros gave $27.5 million, a record donation at the time, to groups opposing President George W. Bush, as reported by The New Yorker. The move prompted the Republican National Committee to accuse the business magnate of having “purchased the Democratic Party.”

Soros, born in Hungary and the founder of what was once one of the world’s largest hedge funds, is the 26th wealthiest person in the world with a net worth of $24.4 billion, according to Bloomberg.