The latest financial disclosures from the liberal Priorities USA Action super PAC contained one particularly surprising contribution: $300,000 from Samuel Rawlings Walton, grandson of the famously conservative founder of Wal-Mart. 

The Sept. 10 gift stands in contrast to several other 2012 donations from Walton clan members, who have spent big in favor of conservative and Republican causes for years. An uncle and two aunts, for example, gave five- and six-figure donations to super PACs backing Republican nominee Mitt Romney and one of his GOP challengers, Jon Hunstman Jr. 

One of the aunts, Alice Walton, was even more active in Republican politics in years past, doling out $2.6 million in 2004 to an independent group that ran ads in support of incumbent George W. Bush.

As Forbes noted Tuesday, 44-year-old Sam Walton -- grandson of the retail chain's founder of the same name and son of S. Robson Walton -- has long leaned left compared to the rest of his family, sitting on the board of the Environmental Defense Fund and donating $30,000 to Obama's campaign in 2008. But the $300,000 contribution marks a significant increase in his involvement and will help pay for anti-Romney ads that Priorities is airing in key swing states over the final days of the campaign. 

This isn't the first wealthy family to show public disagreement over politics this year. TD Ameritrade founder and Chicago Cubs co-owner Joe Ricketts has spent more than $12 million on efforts to defeat Democrats this cycle; he was offered (and rejected) a proposal to run racially-charged ads against Obama. His daughter Laura, meanwhile, is a top Obama bundler and prominent LGBT activist. Chicago's wealthy Crown family is also divided between active Obama and Romney fundraisers, records show.