ATLANTA -- When President-elect Donald Trump takes office in January, Republicans will have the opportunity to pull off something they have wanted to do for years: overhaul Medicaid, the program that provides health care to tens of millions of lower-income and disabled Americans.

Any changes to the $500 billion-plus program hold enormous consequences not only for recipients but also for the states, which share in the cost.

Trump initially said during the presidential campaign he would not cut Medicaid, but later, he expressed support for an idea pushed for years by Republicans in Congress: sending a fixed amount of money each year to the states in the form of block grants.

Backers say such a change in the Medicaid formula is one of the best ways to rein in spending, but critics say big cuts would follow.

Currently, the federal government pays an agreed-upon percentage of each state's Medicaid costs, no matter how much they rise in any given year.

Republicans have argued states have little incentive to keep expenses under control, because no state pays more than half the total cost.

House Speaker Paul Ryan and Trump's pick for secretary of health and human services, Georgia Rep. Tom Price, want to switch to block grants.

Key questions facing Republicans will be how the funding is structured and how much flexibility will be given to the states.

"It's exciting because you know it's not going to be the same as it was, and it's nerve-wracking because you know it's not going to be the same as it was," said Terry England, a Republican state lawmaker who chairs the House budget committee in Georgia.

Republican control of Congress and the presidency means the GOP can act on its long-held priorities of reining in entitlement programs and repealing President Barack Obama's health-care law, which allowed states to expand the number of people eligible for Medicaid. Thirty-one states have opted for the expansion.

It is not clear what the GOP's replacement plan will look like. Democrats have warned of dire consequences, and any proposed changes are likely to trigger a fight in Congress.

Last week, the Democratic Governors Association warned repealing the Affordable Care Act would end health coverage for millions of people and shift the financial burden onto the states, costing them $68.5 billion in uncompensated care over the next decade.

The group said the Medicaid expansion alone has provided coverage for millions of Americans who lacked insurance and been a critical tool for states in combating the opioid epidemic.