The Senate version of President Donald Trump’s massive tax and immigration spending plan would wipe out many of the strides made by the Affordable Care Act in reducing the number of uninsured Americans, resulting in at least 17 million Americans losing their health coverage, according to nonpartisan estimates and experts.

The bill, which narrowly passed the Senate on Tuesday and now heads back to the House, would effectively accomplish what Republicans have long failed to do: unwind many of the key components of the ACA, President Barack Obama’s signature domestic achievement that dramatically increased the number of Americans with access to health insurance.

To start, the Congressional Budget Office estimated that the Senate version of the bill would result in 11.8 million more uninsured in 2034, mostly because of Medicaid cuts, compared with 10.9 million if the House version became law.

In addition, both versions of the bill would allow pandemic-era enhanced subsidies for health insurance through ACA marketplaces to expire at the end of the year, sharply raising out-of-pocket costs for millions of Americans. The CBO estimates that 4.2 million people would lose insurance as a result. An additional 1 million are likely to become uninsured because of a combination of other Trump administration cuts and the Republican legislation, according to the CBO.

The bill also includes other, less-noticed changes that over several years would make it harder for states to maintain the ACA’s Medicaid expansion at existing levels, which currently cover some 20 million Americans, according to KFF, a health policy research organization.

“This bill — if passed, and if the enhanced subsidies expire — will be a very effective undermining of the vision of the Affordable Care Act to move the United States to a country where universal coverage is in sight,” said Joan Alker, executive director of Georgetown University’s Center for Children and Families. “This was the 100-year fight to get to the passage of the Affordable Care Act.”

Trump has long said he would not make cuts to Medicaid and has maintained that the spending package targets only waste, fraud and abuse. But the severe reductions to the program and estimated coverage losses undermine Republicans’ arguments that they are making limited cuts.

Vice President JD Vance dismissed criticisms of the Medicaid provisions in the bill and urged Republicans to focus on its immigration measures.

In a post on X, he argued that “the CBO score, the proper baseline, the minutiae of the Medicaid policy — is immaterial compared to the ICE money and immigration enforcement provisions.”

About 44 million people are enrolled in health care coverage because of the ACA, including its Medicaid expansion and health insurance marketplaces, according to a KFF analysis from earlier this year. Republicans have tried to repeal the law since it passed in 2010. During Trump’s first term, the party’s effort to gut Obama’s health care law was so unpopular that, after it failed because of opposition from Sen. John McCain (R-Arizona), Republican leaders decided it was a loser of an issue and said they would not take it up again.

This time, the dramatic cuts are part of a much larger tax and spending package that seeks to codify trillions of dollars in tax cuts from Trump’s first term that primarily benefit the wealthy, along with hundreds of billions of dollars in new spending on immigration enforcement and national defense. Republicans have proposed paying for those provisions largely by slashing Medicaid.

The Republican bill, if enacted, would mark the biggest cut to Medicaid in the program’s nearly 60-year history and the biggest reduction in federal funding for the social safety net since at least the 1990s. The Senate version would cut $1.1 trillion of federal spending for Medicaid, Medicare and the ACA marketplaces, with Medicaid accounting for more than $1 trillion of the cuts.

The bill “will move us as a nation back to the same percentage of uninsured before Obamacare,” Sen. Mark R. Warner (D-Virginia) said Sunday on CBS. “And it’s not like these people are not going to get sick. They’re going to show up to the emergency room. Rural hospitals are going to be shut down.”

The changes to Medicaid have been a sticking point among Republicans trying to ram through the bill so that it passes by Trump’s self-imposed July 4 deadline. Several Republican senators, including Thom Tillis (North Carolina), Josh Hawley (Missouri) and Jim Justice (West Virginia), have raised concerns about the impact the cuts would have on their states, particularly on already struggling rural hospitals that could be forced to close or dramatically cut back services. Tillis said he opposed the bill because of its Medicaid cuts and announced he would not seek reelection.

“It is inescapable this bill will betray the promise Donald Trump made,” Tillis said in a Senate floor speech Sunday. “What do I tell 663,000 people in two years, three years, when President Trump breaks his promise by pushing them off of Medicaid because the funding’s not there anymore?” Tillis was referring to estimates of how many people in North Carolina would lose Medicaid coverage under the bill.

Trump’s bill proposes implementing onerous work and reporting requirements for Medicaid that would throw millions of people off their health insurance — including some who meet the requirements or qualify for exemptions, according to experts and health providers. Able-bodied adults ages 19 to 64 would have to complete at least 80 hours of qualifying work a month to maintain their coverage, which health providers and experts said would be difficult for many poor residents in areas that have few job opportunities or that rely heavily on seasonal and hourly work. Many states are ill-equipped to sift through reams of additional paperwork to determine whether Medicaid recipients are meeting the new requirements or qualify for exemptions.

The Senate added a measure that reins in a financing maneuver that hospital groups say would slash payments to their facilities — especially rural hospitals. That reduction in what is referred to as the provider tax, along with restrictions on state-directed payments, would cut an additional $375 billion in federal Medicaid spending.

“The repeal bills from 2017 had multiple features. They undid large parts of the Medicaid expansion and decimated the marketplaces. And over time, that is the effect that we’ll see this bill having,” said Allison Orris, senior fellow and director of Medicaid policy at the Center on Budget and Policy Priorities, which opposes the bill. “There’s certainly a lot of outrage and concern about this bill, but if it had been wholly health care focused, we would see a different reaction to it.”