With Republican control of the U.S. House, Senate and White House solidified under a presumptive Donald Trump administration, the 1.2 million Texans with health insurance under President Obama’s signature Affordable Care Act face an uncertain future.

The health law, known as Obamacare, has survived two major Supreme Court decisions and fierce Republican opposition since it passed in 2010. But with Republicans firmly in control come January, conservatives will finally have their chance to repeal major portions of the measure that helps pay for health insurance for millions of Americans. They also stand poised to make sweeping changes to the health care market that could be felt by more than 5 million Texans, many of them children, with government-subsidized health coverage.

Texas leaders were swift to hail Trump’s victory over Democratic challenger Hillary Clinton as a chance to kill the federal health reforms they have opposed for nearly a decade.

“Here’s what we can see coming, and that is the repeal and replacement of Obamacare,” Gov. Greg Abbott said in a telephone interview Wednesday, before listing other targets of GOP ire, including environmental and business regulations championed by the Obama administration. “What I see is this is going to be tremendous spur to the economy.”

A total repeal of the Affordable Care Act, as urged by Abbott, U.S. Senator Ted Cruz and other leading Texas Republicans, appears unlikely without a 60-vote Republican supermajority in the U.S. Senate. Democrats will likely use Senate filibuster rules to block any such attempt. Talk of replacing the Affordable Care Act, too, could easily fall short without a Senate supermajority for Republicans.

But previous, Republican-led attempts in Congress to undermine the health law offer an example of the sorts of major — if incomplete — changes that could be possible in the early days of a Trump presidency.

The U.S. House and Senate last year passed a budgetary process bill that would have rolled back major portions of the Affordable Care Act without repealing it entirely. Known as a budget reconciliation bill, the measure can be passed by a simple majority and cannot be stopped by a Senate filibuster.

Last year’s reconciliation bill, which Obama vetoed, would have eliminated Affordable Care Act funding that helped pay for health insurance for low- and middle-income Americans, both through Medicaid coverage and subsidized private insurance bought on Healthcare.gov. It would have ended tax penalties for people who did not have health insurance, a part of the law meant to encourage people to sign up for coverage. It would have defunded Planned Parenthood and cut several taxes that helped pay for the law’s coverage expansion.

If that attempt at a partial repeal is any indication, about 22 million Americans could lose health insurance under a Trump presidency, according to a nonpartisan analysis by the Congressional Budget Office, including many of the 1.2 million Texans with Obamacare plans who could not afford them without subsidies.

Texas did not offer expanded Medicaid coverage to poor adults, so that provision of the law, even if repealed, would not directly affect the Lone Star State. Other parts of the sweeping health law, such as provisions that allow children to stay on their parents’ health plans until age 26 and rules that require health insurers to cover certain benefits, would not be touched by the budget reconciliation process.

For now, uncertainty reigns among doctors, hospital administrators and other health care providers. In the hours after Trump’s victory, stock prices for hospitals and health insurance companies tumbled.

“It’s a brave new world for all of us, eight years after it was another brave new world with the passage of Obamacare,” said Tom Banning, chief executive of the Texas Academy of Family Physicians, an advocacy group.

Patients, too, are grappling with the uncertainty. People with Affordable Care Act coverage “are deeply worried about what the election results mean for their health, their families and their financial security,” said Anne Filipic, president of the nonprofit Enroll America, which encourages people to sign up for health insurance, in an emailed statement.

Still, she said, “Right now, it is critically important to reassure consumers that nothing has changed.”

Even the staunchest opponents of the Affordable Care Act say changes made to the law will take years to implement. The 2015 budget reconciliation measure, for example, would have waited two years before taking effect.

“No matter how disruptive [Trump] wants to be and how much change he wants to implement, it’s going to take quite a bit of time,” said Deane Waldman, director of the Center for Health Care Policy at the Texas Public Policy Foundation, an influential, conservative think-tank.

Immediately after his victory, Trump published a plan for his first 100 days in office, which includes a pledge to “fully” repeal Obamacare and replace it “with Health Savings Accounts [and] the ability to purchase health insurance across state lines.” The plan also pledges to let states manage Medicaid funds from the federal government, reminiscent of conservative policy proposals that call for Medicaid block grants. Such a proposal would allow states to spend federal health care dollars with fewer rules governing how many people Medicaid must cover and what benefits the program must offer.

“If we follow these steps, we will once more have a government of, by and for the people,” the proposal says.

Block grants have long been a favored policy tool among Texas Republicans, who say the Medicaid program’s costs are unsustainable. Last year, state Sen. Charles Schwertner, R-Georgetown, stood alongside Lt. Gov. Dan Patrick and other Republican leaders at a press conference to ask for a Medicaid block grant from the Obama administration. Their demands went nowhere.

Similar requests by former Gov. Rick Perry for flexibility in spending Medicaid dollars failed under both Democratic and Republican presidents. About 4.4 million Texans are currently on Medicaid, most of them children. Texas’ eligibility requirements for non-disabled adults to receive Medicaid coverage are among the strictest in the nation.

In 2008, Perry asked health officials under President George W. Bush for a waiver allowing the state to limit its number of Medicaid beneficiaries and create a less generous benefits plan. That request was rejected.

And in 2011, Perry signed legislation asking the feds for a Medicaid block grant, a capped amount of money that would have come with more flexibility for the state to toy around with spending. That proposal also hit a dead end.

A spokesman for Schwertner did not respond to a question about the senator’s plans for a Medicaid block grant under a Trump administration.

Waldman, of the Texas Public Policy Foundation, said it was too early to tell how much freedom to administer Medicaid would come from a block grant under the Trump administration.

“I know there is interest in this” among state lawmakers, he said. “I am not sure that there is any consensus as to how much control we can reacquire, and that’s really the big issue.”

Anne Dunkelberg, associate director of the left-leaning Center for Public Policy Priorities, said Texas elected officials still had several questions left to answer about what they would do with a Medicaid block grant.

“In actual governance, you have to figure out what it is you’re trying to accomplish with the block grant,” she said. “Do you want to serve fewer people? Do you want to provide people with fewer benefits? Do you want to pay providers even less than you’re paying them now?”

Read related Tribune coverage:

• The roughly 1.3 million Texans who bought health insurance under the Affordable Care Act will likely have fewer, more expensive coverage options in 2017, as health plans continue to announce they will no longer sell their products in Texas.
• A new study finds that the rate of children in Texas without health insurance continues to fall, but the state still leads only Alaska in getting children covered.
• Comments by high-ranking Texas Republicans indicate that the state’s long-running tug-of-war with the federal government over Medicaid expansion is unlikely to change course.

Patrick Svitek contributed to this report.

Disclosure: The Texas Public Policy Foundation and Center for Public Policy Priorities have been financial supporters of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.