President Obama's march to $1 billion in campaign cash continues, as a combination of small donations and effort by fundraising heavyweights garnered the president $46 million in the second quarter.

Slightly fewer than half of the contributions were less than $250, a sign that Obama's grassroots network remains vibrant. But he also benefited from bundlers, influential figures who are able to pull in money from different sources and who contributed the bulk of the money with $37 million. The Obama Victory Fund, a joint fundraising vehicle, raised more than 50 percent of its total from donors maxing out at $35,800 and more than 90 percent from donors giving $10,000.

Money is likely to play an outsized role in this election, particularly with the Citizens United U.S. Supreme Court decision opening up torrents of untrackable donations. Obama initially disparaged the stampede of special interest money that helped propel Republicans to sweeping gains in 2010, but since then Democrats have worked to build a formidable fundraising machine that will also rely on massive undisclosed funding. The powerful Republican political action committee cast 2012 as a David and Goliath battle given the Obama campaign's virtually limitless financial resources.

Obama has also worked to court the Wall Street donors who were among his top backers in 2008, inviting high profile financial executives to the White House and attending fundraising events. His support for the Dodd-Frank financial reform bill and some rhetoric critical of the financial industry has damaged his standing somewhat in the business community. According to a Huffington Post analysis, nobody has emerged yet as a disproportionately large source of donations to Obama.

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