Barack Obama is braced for a barrage of attacks from a political campaign group founded by former aides to President George W Bush and backed with tens of millions of dollars in corporate funding.
American Crossroads, the most powerful "Super PAC" [political action committee] aiming to oust the president in November, is preparing a blitz of television advertisements in key states.
The group, which was created by Bush's former chief strategist, Karl Rove, can collect unlimited donations from corporations thanks to a Supreme Court ruling that backed the independent campaign groups.
Several are poised to assist Mitt Romney, the presumptive Republican presidential nominee, with an onslaught against Mr Obama.
American Crossroads alone raised more than $50?million (pounds 31.5?million) last year, and plans to spend up to $200?million (pounds 126?million) on the 2012 election. The main Super PAC backing Obama, Priorities USA Action, has raised $6.5?million (pounds 4.1?million).
"It's been remarkable," said Steven Law, the president of American Crossroads. He said that donors were desperate for political change. "They obviously believe that a change needs to happen, and as a result of that they've been very free with their support."
The group is expected to broadcast its first attack adverts by the end of the month, amid concerns among Right-wing activists that the bitter Republican primary campaign has helped Obama.
Law said the endless infighting between Romney and his rivals Rick Santorum and Newt Gingrich was "certainly one of" the reasons the president was leading in opinion polls of swing states. "Every day that goes by that we're not talking about President Obama is a wasted day," Law said.
A Washington Post-ABC News poll last week found that Romney has grown more unpopular as the Republican primary contest has gone on. While 53% of Americans hold favourable views of Obama, just 34% say the same for Romney. Half of voters have a negative opinion of the former Massachusetts governor - a higher number than Obama has ever suffered.
Super PACs were freed to collect unlimited donations from businesses under a Supreme Court ruling in 2010. The court effectively stated that under the US constitution's guarantee of freedom of speech, corporations, like individuals, are able to exercise their right to free speech by donating money.
American Crossroads financial firepower comes largely from a small group of conservative billionaires with strong ties to Rove and the Bush administration.
Topping the list is Harold Simmons, a Texan industrialist who has so far donated at least $10?million (pounds 6.3?million). Simmons has financed conservative causes since the 1980s, when he donated money to the legal defence funds of two aides to President Ronald Reagan charged with selling weapons to Iran.
He also poured money into Swift Boat Veterans for Truth, a political group that savaged John Kerry's Vietnam War record during the 2004 election and is credited with helping Bush's victory.
American Crossroads has also received at least $9.5?million (pounds 6?million) from Bob Perry, a Texan building tycoon who also contributed heavily to the Swift Boat campaign. Perry helped finance Bush's campaigns to become governor of Texas in the Nineties and is also a major contributor to Restore Our Future, a Romney-supporting Super PAC that has been credited with destroying the Republican primary prospects of Gingrich.