Billionaire financier George Soros has promised $1m to the "Super PAC" group that is helping fund President Barack Obama's re-election bid.
The move could trigger more large cheques from liberal donors who have avoided giving to Super PACs, due to their concern over the unlimited spending power of such groups.
Until this year, Soros held the record as the biggest contributor in an election cycle for his 2004 political donations, valued at some $27.5m.
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