(Bloomberg) — The Affordable Care Act replacement plan put forward by Senate Republicans would increase the number of uninsured Americans by 22 million while slashing funding for Medicaid, according to an estimate by the Congressional Budget Office.

The Senate bill, called the Better Care Reconciliation Act, would reduce the deficit by $321 billion over a decade, according to the CBO, which provides nonpartisan analysis of legislation for lawmakers. That compares with a bill that passed the House of Representatives in May, which CBO at the time projected would result in 23 million fewer people with insurance and cut the deficit by $119 billion.

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The biggest increase in the uninsured would come from the bill’s roll back of Medicaid, the state-federal program that covers the poor. The GOP bill cuts spending on Medicaid by $772 billion over a decade, and would result in 15 million more people uninsured by 2026 than under current law. Another 7 million wouldn’t have coverage in the individual insurance market.

CBO estimated that the law would lower insurance premiums in the long term, but raise out-of-pocket costs. Premiums would rise over the next several years and then fall, relative to current law. In 2026, average premiums would be about 20 percent lower than they would be under Obamacare. That’s in part because coverage would be skimpier, and individuals would face higher deductibles and other cost-sharing.

“Because nongroup insurance would pay for a smaller average share of benefits under this legislation, most people purchasing it would have higher out-of-pocket spending on healthcare than under current law,” CBO said.

The findings set the stage for a short yet intense debate among Republicans, with Majority Leader Mitch McConnell having to win over 50 of his 52 Republican Senators to get the bill passed this week. The scale of the Medicaid cuts and the increase in the number of people without insurance may give pause to moderate senators. Nevada’s Dean Heller has already said they won’t vote the current version of the bill. A block of four conservatives also opposed the proposal, but for different reasons: They said the bill doesn’t go far enough in undoing Obamacare.

“I’m very concerned about the cost of insurance for older people with serious chronic illnesses, and the impact of the Medicaid cuts,” Maine Senator Susan Collins, a key Republican moderate, said Sunday on ABC’s “This Week” with George Stephanopoulos. “I have very serious concerns about the bill.”

The Senate bill would reduce taxes on the wealthy, as well as on insurers, drug companies, device makers and tanning salons, paying for it with sharp cuts to the Medicaid program for the poor and with reductions to the subsidies that help middle-class people buy insurance on their own. The tax cuts are nearly identical to those proposed in the House’s Obamacare repeal bill.

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