WASHINGTON - The 2012 presidential contest is expected to cross the $2 billion fundraising mark Thursday.

Donations supporting the candidacies of President Barack Obama and Republican challenger Mitt Romney have so far exceeded $1.5 billion through September. That figure doesn't count more than $230 million flowing to independent "super" political committees working to get them elected.

Updated financial reports showing fundraising tallies are due to be filed by the end of the day. They're likely to show how ordinary citizens and billionaires alike are fueling what's expected to be the costliest campaign in history.

Wealthy Americans have contributed generously this election to super PACs. Those groups can raise unlimited sums of cash and have spent hundreds of millions of dollars on TV ads.