The law envisions that insurers will be able to accommodate older and sicker people without facing financial ruin because of its most disputed element, the requirement that Americans have insurance or pay a penalty.
By 2019, about 95 percent of the country will have health insurance if the law is allowed to take full effect, the Congressional Budget Office estimates.
Reams of court filings attest that the changes are being counted on by people with chronic diseases, touted by women who have been denied coverage for their pregnancies, and backed by Americans over 50 but not yet old enough to qualify for Medicare, who face age-inflated insurance premiums.
Republicans are leading the fight to kill the law either by the court or through congressional repeal. They say the worst fears about what they derisively call "Obamacare" already have come to pass in the form of higher costs and regulations, claims that the law's supporters dispute.
The White House says it has little doubt the high court will uphold the law, and that even its opponents will eventually change their tune.
"One thing I'm confident of is, by the end of this decade, we're going to be very glad the Republicans termed this 'Obamacare,' because when the reality of health care is in place, it's going to be nothing like the kind of fear-mongering that was done," said David Plouffe, a senior adviser to the president, said Sunday in an interview with ABC's "This Week."
Polls have consistently shown the public is at best ambivalent about the benefits of the health care law, and that a majority of Americans believe the insurance requirement is unconstitutional.
Associated Press writers Pete Yost, Jesse Holland and Jessica Gresko contributed to this report.
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