(Priorities USA Action/You Tube)

Interest groups closely linked to both parties revealed a bevy of financiers who wrote six- and seven-figure checks to back Republican and Democratic candidates in disclosure documents filed over the weekend.

The filings come at the start of a presidential contest that is expected to be awash in spending by monied interest groups — a contrast to the 2008 election cycle, which largely offered a reprieve from interest-group spending backed by wealthy donors.

The big contributions, which largely come from a handful of party stalwarts, show how top donors on both sides of the aisle are willing to invest in campaigns with the Democratic Senate majority in the balance and the presidency at stake in 2012. The reports show a Democratic donor base that appears to be much more engaged after a 2010 midterm election dominated by new Republican groups.

In the presidential contest, Priorities USA, a group that two of President Obama’s former aides formed to support his reelection bid, said it raised $5 million in the first half of the year, including $2 million from Hollywood producer Jeffrey Katzenberg, the chief executive of DreamWorks Animation and a longtime Democratic Party donor.

Other top contributors have given millions to Democrats in the past, including $500,000 each from newspaper publisher and philanthropist Fred Eychaner and the Service Employees International Union, the reports show.

Priorities USA spent $724,000 on advertising in the first half of the year, including ads attacking Republican candidate Mitt Romney in South Carolina.

“We’ve invested in early advertising to highlight Republican proposals to end Medicare,” said Bill Burton, a founder of the group.

The Restore Our Future PAC, which is supporting Romney, revealed that its $12 million in contributions came from a handful of donors — including hedge-fund founder John Paulson, who gave $1 million.

Other top donors include $1 million from two members of the Marriott hotel family, which has a long connection to Romney and his father, and $2 million from two corporations linked to officials with the cosmetics company Nu Skin Enterprises.

The group has spent only $22,000 since it formed, leaving almost all the money it raised on hand to attack Romney’s GOP rivals and Obama, according to the group’s filing.

“We’re proud of the support Restore Our Future has received from across the country,” said the group’s treasurer, Charlie Spies, who was the general counsel for Romney’s 2008 bid. “These donors recognize Mitt Romney is the most experienced and qualified candidate to challenge President Obama’s record of out-of-control big-government spending, which has led our country to a historic $14 trillion debt and near double-digit unemployment.”

Two conservative organizations, American Crossroads and Crossroads GPS, founded with backing from Bush political adviser Karl Rove, have been running $20 million worth of ads attacking Obama on his handling of the economy. American Crossroads reported donations that include $100,000 from John Templeton Jr., son of the billionaire investor and mutual fund pioneer.

“Crossroads currently has about a 2-to-1 lead over all these groups combined, but we expect the left will eventually outspend us once the cash-rich unions kick into gear,” said Jonathan Collegio, a spokesman for the two groups.

Two Democratic groups focused on congressional races announced they had raised $2.3 million in the first six months of 2011, including large donations from a Nevada businessman and the McKay family, heirs to the Taco Bell fortune.

The group American Bridge 21st Century, which is funding research on Republican candidates, raised $3 million with donors, including party stalwarts Susie Buell and Peter Lewis.

Steven Bing, a movie producer and real estate developer, donated $150,000 to American Bridge and $250,000 to Majority PAC.

All of the groups are highly dependent on wealthy donors who can cut big checks, but some of them also reported small contributions as well. Garrison Keillor,a writer and radio personality, donated $250 to the Democratic Senate group Majority PAC.

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