WASHINGTON—U.S. Rep. Hank Johnson was going over the day's business in a House Democratic caucus meeting Thursday morning when someone in the room repeated a false report that the Supreme Court had struck down the centerpiece of the Affordable Care Act.

A saddened Johnson, of DeKalb County, left the room to collect his thoughts. But by the time he got to his office the mood had shifted to one of joy at the Supreme Court's surprise decision to uphold the mandate that all individuals buy health insurance under Congress' taxing authority.

"This is going to impact America profoundly," he said. "To bring this many people into the health care system is a great step for Americans who are living now, as well as our children and our grandchildren."

For Democrats, it was a moment of vindication for the legislative wrangling to pass the 2010 law. For Republicans, it was a moment of shock and dismay, but also of renewed vigor to overturn the law.

"It's a sad day for liberty in America," said Rep. Paul Broun of Athens, a general practice physician who has pushed his own market-oriented health insurance proposal.

Broun added: "I hope that it is not only going to help us remove a president who has in many ways been acting in a very dictatorial manner, but hopefully it will help us elect a U.S. Senate to help us repeal Obamacare."

The moment itself was one of confusion.

Several hundred people — a mix of the law's supporters and opponents. plus curious onlookers — gathered on the Supreme Court's steps to await the news.

Shortly after 10 a.m., as Chief Justice John Roberts read the decision inside, the masses checked their phones and tablet computers for news, getting conflicting reports.

The first triumphant roar came from the tea party section, with yellow "Don't Tread on Me" flags waving, their holders chanting, "The Constitution matters!" A group of anti-abortion activists — who say the law allows backdoor public funding for abortion — started singing "Amazing Grace."

The law's supporters looked dispirited until one young man correctly yelled out, "The mandate is upheld!" The ensuing pandemonium included chants of "USA!"

The opponents regained control via a louder speaker system, explained what they could of the decision and registered their outrage.

U.S. Rep. Phil Gingrey, a Republican from Marietta, was among the people to seize the microphone, exhorting the crowd not to give up the fight.

"It is our responsibility now to do everything in our power — everything in our power — to repeal Obamacare and to elect Mitt Romney the 45th president of the United States," Gingrey said. "That's the way we can get this job done, absolutely. They may have ruled that this bill, this law is constitutional, but it is un-American."

House Republicans immediately set up a vote to repeal the law July 11. A previous vote languished in the Democratic-controlled Senate.

Romney gave a brief speech on the law two blocks away. He has pledged to immediately grant state waivers from the law if elected and to push a full repeal through Congress.

Georgia Attorney General Sam Olens was in Washington on Thursday morning awaiting the ruling. Olens filed suit on Georgia's behalf against the law and attended the Supreme Court arguments.

Legally, the plaintiffs came out pretty well, he said, as the court ruled in their favor that the individual mandate was unconstitutional under the Commerce Clause and also allowed states to opt out of the law's Medicaid expansion.

But Olens called Roberts' majority opinion "scary" for opening up limitless taxing power — even if the law is not framed as a tax.

A George W. Bush appointee in 2005, Roberts set himself up to take considerable conservative flak, but Georgia's Republican senators, Johnny Isakson and Saxby Chambliss, said they did not regret voting to confirm him.

Chambliss summed up Roberts' reasoning as: " 'We should be careful about overturning laws that Congress does have the authority to enact, and under the Commerce Clause this is a tax. Congress has authority to raise taxes, and that's exactly what they did.' And that's the genesis of his rationale, and I respect it."

Republicans and Democrats each saw the ruling as politically beneficial to their side. The GOP gained a new way to frame the law as a massive tax increase, while Democrats said the approval of the high court should give the law a new stamp of legitimacy.

Democratic Rep. David Scott of Atlanta said there are ways to improve the law, but he was "pleasantly surprised" that it will stand.

"It legitimizes and reinforces an excellent framework that the Obama administration and the Congress laid out," Scott said. "I think we will see a little more pep in the step of the American people now."