WASHINGTON — President Barack Obama’s health-care overhaul is on the way to its ultimate jury — the families, doctors, business people and state officials who will have to grapple with the confusing details while striving to fulfill its promise.

With the Supreme Court hurdle cleared, open enrollment for millions now uninsured is scheduled to begin in just 16 months, in October 2013. Much of the health care industry is ready. People who do have insurance won’t have to worry about the loss of popular new benefits, such as coverage for young adult children or improvements to Medicare’s prescription plan.

And, starting in 2014, insurance companies no longer will be able to turn away people with a history of medical problems, or charge them more.

But carrying out the law will be a mad scramble for states, especially Republican-led ones where officials had hoped this day wouldn’t come. And the court added a new complication by giving individual states more leeway to turn down the law’s expansion of Medicaid, expected to provide coverage to about 16 million uninsured people.

After the ruling, chances of repealing the entire law appear much slimmer for Republicans, although they will again make it an election rallying cry. However, a targeted repeal strategy aimed at individual components of the law, including cost controls, taxes and spending cuts, may still work.

Vicki McCuistion of Driftwood, Texas, who has two part-time jobs and is uninsured, said the Supreme Court ruling has given her new hope.

Her husband has back problems so bad he can’t go to work some days, and with a family history of skin cancer she is worried about a mole that she hasn’t been able to get checked by doctors.

“Having access to health insurance that we can actually afford would allow us to improve our lives,” McCuistion said Thursday.

At the White House, Obama repeated his promise that the Affordable Care Act will deliver health insurance and help get a handle on growing costs.

But the glow of victory may be brief. Even some supporters of the law admit that it is only a first installment, a way to get most of the population covered before tackling costs forcefully. Wrenching choices about Medicare and Medicaid cuts could come as early as next year.

Thursday’s decision moves the United States closer to other economically advanced countries that for years have guaranteed health insurance to their citizens.

The law is expected to extend coverage to about 30 million of the estimated 50 million uninsured; illegal immigrants will represent a large share of those still without coverage.

The focus now quickly shifts from Washington to the states.

While health insurers, big hospitals and major employers have spent the last two years planning and carrying out the law, states are all over the lot.

Although they are expected to play a crucial role in delivering insurance to their residents, only 14 states, plus Washington, D.C., have actually adopted a plan for doing so.