President Barack Obama and his rival Mitt Romney are on track to raise more than $2 billion by Election Day – making it by far the most costly presidential race in history.

By November 6, both candidates will have each passed the $1 billion barrier in donations.

Barack Obama is already there, according to financial disclosures filed yesterday. The president and his Democrat Party have tallied up about $1.06 billion while Mitt Romney and the Republicans have collected $954 million since the turn of the year.

By comparison, Barack Obama raised a total of $750 for his successful 2008 campaign and his opponent, John McCain, raised just $130 million, which included a government grant for more than two-thirds of the total.

The sources of the money underline the difference between the two rivals and the kind of support they are attracting.

Wall Street has invested more heavily in Mitt Romney than any White House candidate in memory, according to the New York Times, which obtained the disclosures last night. Employees of financial firms have given more than $18 million to the ex-financier’s campaign.

They have also donated hundreds of millions more to so-called “super PACS” – groups working independently of the official campaigns that often provide cash for adverts backing their chosen candidates. The super PAC cash is not included in the campaign totals.

Doctors, insurance companies, accounting and property firms are all turning more to the Republican hopeful than they did four years ago.

Barack Obama has set his sights more on Silicon Valley and it has clearly paid off with technology executives donating $14 million to his coffers, much more than last time around.

Retirees – the biggest source of money for both sides – as well of employees of retailers, hospitals, nursing homes and women’s groups have all sided in bigger numbers with the Democrat incumbent.

Barack Obama and his rival Mitt Romney are on track to raise more than $2 billion by Election Day

Like in 2008, the vast majority of Barack Obama’s money came in small donations – 55% of his donations came in amounts of less than $200. Just 13% of his cheques were for $2,500, the maximum amount donors are allowed to give as individuals.

The Obama campaign has received donations from 4.2 million people, about a million more than in 2008.

By contrast, Mitt Romney has profited from support from big business donors. Just 22% of his cash came from people donating less than $200 while 45% was for the $2,500 maximum.

Of the super PACS, Mitt Romney was by far the biggest winner. Groups aligned with Mitt Romney have spent $302 million on campaign advertising, compared with about $120 million for groups supporting Barack Obama.

Wrapping up a 40-hour battleground state blitz yesterday, Barack Obama headed to his hometown of Chicago and cast his ballot 12 days before Election Day.

The stopover was more than a photo opportunity – it was a high-profile attempt to boost turnout in early voting, a centerpiece of the president’s strategy

Michael Toner, a Republican campaign finance lawyer and former chairman of the Federal Election Commission, said the close race between Barack Obama and Mitt Romney and the sharply polarized electorate have also played a role in accelerating the dash for dollars.

“I don’t know any campaign manager who thinks they have too much money. In this political 50-50 environment you can’t ever have enough,” Michael Toner said.

“Every last million could make the difference in who is elected.”

But the emergence of super PACs and other outside groups, emboldened partly by the Citizens United decision by the Supreme Court in 2010, has done more than anything else to reshape the contours of presidential campaign fundraising.

A handful of federal court cases have broadly eased campaign finance regulations, allowing donors to give unlimited sums. That kind of money has largely been funneled to super PACs, which can raise and spend money on behalf of candidates as long as they don’t coordinate expenditures or strategy with the campaign.

“The distinctive factor in this election is the outside money being spent and the corrupting money financing it,” said Fred Wertheimer, a longtime campaign finance reform advocate.

“It’s a symbol of the disastrous campaign finance system we have and the undue influence relatively few well-financed individuals and interest groups now have over government decisions.”

Las Vegas casino mogul Sheldon Adelson is the top super PAC donor this year. Sheldon Adelson, a billionaire, has contributed more than $40 million to Republican super PACs, including those backing Mitt Romney and former candidate and House Speaker Newt Gingrich.