Ahead of the Supreme Court's decision on the Affordable Care Act, President Obama today offered impassioned support for the law's most popular provisions and warned that Mitt Romney opposes them, regardless of how the court rules.

Obama told a crowd of donors at a campaign fundraiser in Atlanta, Ga., that the presumptive GOP nominee would kick "tens of millions of people" off of health insurance rolls, among other steps, to help pay for $5 trillion in new tax cuts for upper-income earners.

"He'd roll back the Affordable Care Act, and he'd block-grant Medicaid in such a way where vulnerable people all across the country, folks who may be disabled, folks - seniors who are relying on those services - that would be eliminated," Obama said.

"But that doesn't pay for $5 trillion. That's not enough," he added, launching into a litany of other tax benefits and services targeting the middle class that he said Romney would slash.

"It ain't right," Obama said. He spoke at the Westin Peachtree Plaza before a crowd of roughly 500 guests, each paying between $250 to $10,000 to attend, a campaign official said. It was Obama's 168th re-election fundraiser since he announced a bid for a second term in April 2011.

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The president conceded to supporters, as he often does, that November will be a very close election driven largely by the economy. But he suggested health care issues could play a decisive role.

"The American people understand that we're not going to make progress by going backwards; we need to go forwards," he said, underscoring his re-election campaign theme. "They understand we don't need to re-fight this battle over health care. It's the right thing to do, that we've got 3 million people who are on their parents' health insurance plans that didn't have it before.

"It's the right thing to do to give seniors discounts on their prescription drugs. It's the right thing to do to give 30 million Americans health insurance that didn't have it before," he said to resounding cheers and applause.

"They want to go forward."