WASHINGTON - President Barack Obama's victory all but assures that his landmark health care law and its guarantee of insurance coverage for all Americans will be implemented, essentially putting an end to the Republican campaign to derail the law.

Starting in 2014, millions of Americans should be able to get health insurance for the first time. Millions more who don't get coverage through work should be able to buy a health plan that meets new basic standards.

"It's all over but the shouting," said Families USA Executive Director Ron Pollack, an influential consumer advocate and leading champion of the law. "What was very questionable at the start of the year has been settled. ... The Affordable Care Act will be a permanent fixture of the American health care system."

That outcome - which seemed almost unimaginable this spring when the Supreme Court considered whether the law was constitutional - puts immediate pressure on many Republican state leaders who fought it. They must decide in days whether to implement it or have the federal government do it for them.

Tuesday's results also present Obama with a new set of challenges as he tries to fulfill the promise of his signature legislative achievement, the biggest expansion of the social safety net since Medicare and Medicaid were created in 1965.

Federal and state officials nationwide must create systems to handle millions of new insurance customers. Key will be setting up insurance marketplaces, known as exchanges, in every state by next October.

And Obama will face renewed pressure to scale back the law as Congress tries to rein in federal budget deficits.

The act authorizes more than $1 trillion in new federal spending over the next decade. Although that is offset with new taxes and other spending cuts, critics say the law's program to provide insurance subsidies to households making up to four times the federal poverty level - or about $90,000 for a family of four - is overly generous.

At the same time, health insurance companies, hospitals, employers and other interest groups are gearing up lobbying campaigns to modify the law, parts of which threaten to push up health care costs.

Also unclear is how the administration will contend with GOP governors who continue to resist the law and may spurn hundreds of billions of federal dollars to provide insurance coverage.

Several states, including Texas, Florida and Louisiana, have indicated they will not open their Medicaid programs in 2014 to cover all low-income citizens. Most states - including those with Republican statehouses -are expected to expand Medicaid because the law provides hundreds of billions of dollars in federal money.

The President could face even more resistance to the law if insurance premiums and other medical costs continue to rise in coming years, undermining a pledge he made in pushing for reform.

"It will be full-speed ahead with implementation. But there could still be some rocky going," predicted Dean Rosen, a Republican health care lobbyist and onetime aide to former Senate Majority Leader Bill Frist.

James Capretta, associate director of the White House Office of Management and Budget under President George W. Bush, said many conservatives would not stop contesting the law. "The fight over the size and scope of government will continue," he said. "Giving up is not an option."