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President Barack Obama wasted little time casting Republican rival Mitt Romney as "backwards on equality" on Thursday, eager to transform his historic embrace of same-sex marriage into donor enthusiasm and grassroots vigor.

Just one day after announcing his support of the top gay rights issue, Obama was attending a lavish West Coast fundraiser hosted by actor George Clooney in Los Angeles' Studio City area, the heart of celebrity gay marriage activism. At the same time, his campaign rolled out a Web video claiming Romney would roll back some rights for same-sex couples

White House spokesman Jay Carney brushed aside questions about the timing of the attack on Romney, saying that Obama and Romney had differed on issues of gay rights even before the president declared his support for same-sex marriage.

"Gov. Romney is for an amendment to the U.S. Constitution that would enshrine discrimination into our founding legal document," Carney said. "The president thinks that's wrong. So their positions were starkly different before yesterday."

In Seattle, where he was attending two fundraisers, Obama witnessed the support first hand as his motorcade passed a woman holding an infant and a sign that said: "Thank you! Mr. President for standing up for my mommys!"

He drew big cheers from supporters at Seattle's historic Paramount Theater when he said his vision for a better America applies to everyone, "no matter what you look like, no matter what your last name, no matter who you love."

Without referring directly to marriage, Obama expanded on the theme of same-sex equality.

"We are moving forward to a country where every American is treated with dignity and with respect and here in Washington you'll have the chance to make your voice heard on the issue of making sure that everybody, regardless of sexual orientation, is treated fairly," Obama said. "You'll have a chance to weigh in on this. We are a nation that treats people fairly."

Washington state has passed a law approving same-sex marriage, but opponents in Washington are gathering signatures for a ballot initiative to overturn the law and declare marriage as union of man and woman.

Outside the Paramount, 44-year-old Teri McClain was holding a double-sided sign expressing gratitude to the president for "evolving on same-sex marriage."

"He's looking out for the good of the people, and this is what the people want," McClain said.

Though the timing of his announcement was not of his choosing, the campaign was not shying away from the issue even though aides conceded it held some political risk for the president. Just hours after Obama voiced his support for gay marriage in an ABC interview, the campaign emailed a clip of the interview and a personal statement from the president to its vast list of supporters, drawing attention to his stance

Still, Obama said Vice President Joe Biden got "a little bit over his skis" in publicly embracing gay marriage, forcing Obama to speed up his own plans to announce support for the right of same-sex couples to marry.

"Would I have preferred to have done this in my own way, in my own terms, without I think, there being a lot of notice to everybody? Sure," Obama said. "But all's well that ends well."

Biden apologized to Obama on Wednesday for getting ahead of him, a person familiar with the exchange said. The person, who spoke on condition of anonymity to describe the private discussion, said Obama accepted the apology and told Biden he knew Biden's own words of support for gay marriage were heartfelt.

Hollywood has been outspoken in its support of gay rights. Although Obama will be in a liberal bastion, California itself illustrates the crosscurrents of gay marriage. Californians have twice voted to ban gay marriage, most recently in 2008. The most recent ban, known as Proposition 8, is being fought in the courts.

Clooney's dinner was organized by Jeffrey Katzenberg, the CEO of DreamWorks Animation, and will include such celebrity guests as Robert Downey Jr. and Barbra Streisand. The event was initially to be a spring gala hosted by Katzenberg at his house. But Katzenberg's home is under renovation, so Clooney offered to host instead.

That prompted the Obama campaign to conceive an online raffle for the general public. Tens of thousands of people participated, drawn by the campaign's pitch: "For a chance to hang out with President Obama at George Clooney's house, donate $3 or whatever you can to be automatically entered to win."

As a result, nearly two-thirds of the money raised for the event will be from people who won't attend. The two winners were Beth Topinka of Manalapan, N.J., and Karen Blutcher of St. Augustine, Fla.

The timing of the event is creating a blockbuster confluence of high celebrity, big money and committed activism. Hollywood is home to some of the most high-profile backers of gay marriage. The 150 donors who are paying $40,000 to attend Clooney's dinner will no doubt feel newly invigorated by Obama's watershed announcement the day before.

The dinner, heavily promoted online by the Obama campaign, is expected to net close to $15 million. That's an unprecedented amount for a single event. And it means that in one single evening the Obama camp and the Democratic Party will collect more than Mitt Romney, the presumed Republican challenger, has amassed in his best single month of fundraising.

In Seattle, Obama expected to collect at least $3 million toward his re-election effort. On Friday, he will fly to Nevada, a highly contested state, where he will call for housing relief in a speech in Reno.

Despite the attempt to turn the campaign page, Obama's support of gay marriage is likely to set the tone for several days. Obama holds a fundraiser Monday in New York sponsored by gay and Latino supporters.

Obama doesn't have the power to make same-sex marriage legal. But his announcement had long been sought by gay rights advocates, who cheered his public affirmation of gay marriage.

Gay marriage remains enough of a divisive issue that there could be political risks. If opposition to gay marriage drives even a sliver of the voting population, it could make a difference in close swing states. Moreover, it could boost fundraising for social conservative groups that are mounting their own campaigns against Obama and galvanize conservatives still uncertain about Romney's commitment to their causes.

"It would be hard to argue that somehow this is something that I'd be doing for political advantage," Obama said in an interview aired Thursday on ABC's "Good Morning America."

"Frankly, the politics, it's not clear how they're going to cut," Obama said.

Romney quickly reiterated his opposition to same-sex marriage. "I believe that marriage is between a man and a woman," he said Wednesday in Oklahoma.

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Associated Press writers Manuel Valdes in Seattle, and Julie Pace and Laurie Kellman in Washington contributed to this report.