In a landmark decision the U.S. Supreme Court upheld President Barack Obama's health care law on Thursday.

The court's 5-4 ruling means the health care overhaul, which is still only partially in effect, can proceed and pick up momentum over the next several years.

It comes three months after the high court heard three days of testimony for and against the Patient Protection and Affordable Care Act.

At the heart of the case was the law's individual mandate which requires most Americans have health insurance or pay a penalty.

The conservative Chief Justice John Roberts, who announced the court's judgment, was the deciding vote on the issue, arguing that the Constitution permits the mandate as a tax.

The court found it constitutional under the taxing power of the federal government, even if it violates the Constitution’s commerce clause.

"It should be pretty clear by now that I didn’t do this because it was good politics. I did it because I believed it was good for the country," Obama said.

In addition to the individual mandate, the bill bans companies from denying coverage based on pre-existing conditions or dropping coverage when someone gets sick.

It also allows children to remain on their parents' policies until age 26.

The justices limited one planned provision of the health care bill, finding problems with the law's expansion of Medicaid.

They ruled the expansion could proceed as long as the federal government does not threaten to withhold a state's full Medicaid allotment if they do not take part in the extension.

Obama signed the bill into law in March 2010, just days after it passed the then-Democrat controlled House by a narrow 219-212 vote.

It had previously passed the Senate by a 60-39 vote.

The high court's ruling is largely seen as a crucial election-year victory for the president.

Both Bloomberg and Senator Charles Schumer suggested the ruling means it is time to put the issue to rest.

"I think by and large the health care system has already adapted to these rules and regulations anyways. So, it's hard to see if anything's really going to change tomorrow. It's just now there is no argument. This is the law," said the mayor. "Congress had the right to pass it. The president had the right to sign it. Now let's get on and make it work."

"Now that all three branches of government have a read on this proposal, the American people are saying, 'Move on,' whether they're for the bill or against the bill," said Schumer. "The number one concern if you read any poll in any part of the country is jobs, the economy, helping the middle class make ends meet. So if either political party spends all its time debating health care or litigating health care, they're going to lose out."

Republicans, meanwhile, dug in their heels.

“I think today’s ruling underscores the urgency of repealing this harmful law in its entirety,” said House Speaker John Boehner.

Speaking in D.C., former Massachusetts governor and GOP presidential candidate Mitt Romney said, if elected, he would work to repeal the health care law.

He says the legislation raises taxes, cuts Medicare and places an unfair burden on businesses.

"Businesses across the country have been asked what the impact of 'Obamacare.' Three-quarters of those surveyed by the Chamber of Commerce say Obamacare makes it less likely to hire people. And, perhaps most troubling of all, Obamacare puts the government between you and your doctor," Romney said.

Echoing Romney's tone, Senate Minority Leader Mitch McConnell says the debate does not end with the Supreme Court's decision.

Thousands of protesters organized by conservative groups immediately took to the streets of Washington, D.C. to rally against the decision.

The demonstrators, who filled the streets near the White House and marched toward the U.S. Capitol, argued the plan raises taxes, cuts Medicare and adds to the deficit.

Back in the city, the Supreme Court decision immediately drew mixed reactions from New Yorkers all across the city.

"This debate about health care has been going on — president after president — for 20-30 years. This guy's finally got something done. I don't know if it's great, but it's better than not doing anything for all that time, so let's give it a shot," said one New Yorker.

"That's terrible. That's too much. How are we gonna afford that? That's a lot. They're asking for too much. That's unfair," said another New Yorker.

House Republicans say they will vote to repeal the law on July 11, even if there is little chance the Democrat-controlled Senate will follow suit.