NEW YORK - It's on.

Independent groups favoring Mitt Romney already are launching TV advertisements in competitive states for the November general election, providing political cover against President Barack Obama's well-financed campaign while the Republican candidate works to rebound from a bruising and expensive nomination fight. Some conservative organizations also are planning big get-out-the-vote efforts, and Romney backers are courting wealthy patrons of his former GOP rivals.

Taken together, the developments underscore how dramatically the political landscape has changed since a trio of federal court cases - most notably the Supreme Court's Citizens United ruling - paved the way for a flood of campaign cash from corporations and tycoons looking to help their favored candidates.

"Citizens United has made an already aggressive anti-Obama movement even more empowered," said Stephen Farnsworth, a professor of political science at the University of Mary Washington. "There's now a regular Republican line of attack on Obama, even when the Romney campaign is taking a breather, raising money and preparing for the general election."

The general election spending - and advertising - has only just begun. Voters in roughly a dozen hard-fought states will be inundated with TV ads, direct mail, automated phone calls and other forms of outreach by campaign staff members and volunteers pleading for their votes. While Obama and Romney both will spend huge amounts of money in the coming months, an untold additional amount will come from outside organizations called super PACs that can collect unlimited contributions from corporations, unions and individuals.

Already, Obama's campaign has spent $3.6 million on commercials in key battlegrounds in the weeks since Romney became the presumptive Republican nominee.

Its latest ad depicts Romney, a wealthy former private equity executive, as a corporate raider who once maintained a Swiss bank account. The president had $104 million on hand at the end of March, giving his campaign a 10-1 advantage over Romney who had just $10 million his campaign bank at the same time.

But Obama is unlikely to receive anywhere near the kind of financial backup Romney is already getting from outside groups. The pro-Obama super PAC Priorities USA Action has raised just $10 million since its inception, and few other Democratic-leaning groups have signaled they plan to compete with the pro-Romney efforts.

The latest of these comes from Restore Our Future, a super PAC run by former Romney advisers.

The group announced Wednesday it will go up with $4.3 million in ads this week in nine states that will be key to winning the White House. The ad, "Saved," describes Romney's efforts that helped lead to the rescue of the teenage daughter of a colleague after she disappeared in New York for three days.

ROF was by far the biggest advertiser during the Republican nominating contest, spending $36 million on ads attacking Rick Santorum and Newt Gingrich. The group has raised more than $51 million since its inception.

Its initial general election push follows a $1.7 million, three-state ad buy from Crossroads GPS. That group's spot attacks Obama's energy policies. And it is an arm of American Crossroads, a super PAC with ties to President George W. Bush's longtime political director Karl Rove and one of the most prolific spenders in the 2010 cycle that put the House in Republican hands. The two Crossroads groups have already raised $100 million collectively for 2012 and plan to spend as much as $300 million to defeat Obama and other Democrats.

Americans for Prosperity, a conservative-leaning independent group backed by the billionaire energy tycoons Charles and David Koch, dropped $6.1 million on ads in eight general election swing states last week hitting Obama for allowing millions in federal stimulus money to be directed to green energy companies overseas. The group spent $6.5 million earlier this year on ads criticizing Obama over Solyndra, a California-based solar energy company that went bankrupt despite a $535 million federal loan guarantee.

AFP president Tim Phillips said the group planned to raise $100 million and that slightly less than half would go to advertising. Much of the remaining amount, he said, would be used for field operations like rallies, bus tours, canvassing, phone banks and micro-targeting.

AFP boasts chapters in 34 states and its field operations have included annual conservative conferences.

Phillips cited Florida, where the group now has a staff of 20 and has promoted bus tours assailing Obama and Democratic Sen. Ben Nelson.

"We use our rallies to let people know how their president and their senators and congressmen are voting on key issues," Phillips said. "A rally focusing on government over-spending can be as effective as a media buy."

The Romney campaign, by contrast, has not run its own TV ads since former Pennsylvania Sen. Rick Santorum dropped out of the GOP nomination fight in April.

Senior Romney aides said they are closely tracking the super PAC ad buys from allies but insist there is no coordination between the campaign and the outside groups.

At the same time, Romney's team also is working to improve relations with Sheldon Adelson and Foster Friess, billionaires who almost single-handedly financed super PACs supporting Romney's opponents during the nomination fight.

Representatives of ROF and other Romney backers have reached out to Adelson, a casino mogul who contributed about $20 million to a super PAC supporting Newt Gingrich. But Adelson has not yet given money to the pro-Romney efforts, and a person close to him said he doesn't want to be a campaign distraction and may give money only to groups like Crossroads GPS and other nonprofit advocacy organizations not required to disclose their donors.

Friess, who helped bankroll a super PAC supporting Santorum, has said he would back Romney and has spoken to Romney supporters.

Romney's campaign concedes that the super PAC activity alleviates financial stress as he works to add staff and raise campaign cash.

His aides are also noting Priorities USA Action's slow start compared to the pro-Romney groups. The disparity is fueling a quiet confidence among Romney advisers who believe that his super PAC support will significantly narrow Obama's current 10-to-1 cash advantage.