WASHINGTON— Twenty-two million Americans would lose insurance over the next decade under the Republican-controlled Senate’s healthcare bill, a nonpartisan congressional office said on Monday, complicating the path forward for the already-fraught legislation.

After the Congressional Budget Office (CBO) score, Senator Susan Collins, a moderate Republican from Maine, said she could not support moving forward on the bill as written.

Collins’ opposition highlights the delicate balance that Senate Majority Leader Mitch McConnell (R-KY) must strike as he tries to deliver a legislative win to President Trump by reconciling the Republican Party’s moderate and conservative wings.

Moderate senators are concerned about millions of people losing insurance. Key conservative senators have said the Senate bill does not do enough to repeal Obamacare.

The CBO assessment that an additional 15 million people would be uninsured in 2018 under the bill and its prediction that insurance premiums would skyrocket over the first two years prompted concern from both sides.

McConnell’s goal had been to have a vote on the bill before the July 4 recess that starts at the end of this week, but said Tuesday he was delaying the vote until after the recess. Several Republicans, including Collins, had said they would not approve a procedural motion that would clear the way for a vote.

McConnell can afford to lose just two Republican senators from the 52-seat majority in the 100-seat Senate, which would allow passage of the bill with Vice President Pence casting the tie-breaking vote.

“If you are on the fence … this CBO score didn’t help you, so I think it’s going to be harder to get to 50, not easier,” Republican Senator Lindsey Graham of South Carolina said of the bill’s prospects.

The CBO score is also likely to amplify criticism from industry groups such as the American Medical Association, which said earlier on Monday that the Senate’s bill violated the doctors’ precept of “first, do no harm.”

The CBO is only able to assess the impact of legislation within a 10-year window, but it said that insurance losses are expected to grow beyond 22 million due to deep cuts to the Medicaid insurance program for the poor and disabled that are not scheduled to go into effect until 2025.

Trump and Republicans in Congress made repealing and replacing the Affordable Care Act (AKA Obamacare), former President Obama’s signature domestic legislation, a central campaign promise. The pressure is on for them to deliver a better alternative to the Democratic former president’s plan, now that they control the White House, the House of Representatives and the Senate.

Republicans view Obamacare as costly government intrusion and say that individual insurance markets are collapsing. Obamacare expanded health coverage to some 20 million Americans by expanding Medicaid and mandating that individuals obtain health insurance.

The CBO score was released just hours after Republicans revised the bill, adding a measure that would penalize people who let their insurance coverage lapse for an extended period. The move followed criticism that the original bill would result in a sicker — and more expensive — insurance pool.

At least four conservative Republicans — Senators Ted Cruz of Texas, Rand Paul of Kentucky, Ron Johnson of Wisconsin and Mike Lee of Utah — have expressed opposition to the Senate legislation.

Moderate Republicans have warned against replacing Obamacare with legislation that is too similar to the version passed by the House, saying it would cause too many people, especially those with low incomes, to lose health coverage.

The CBO estimated that the House bill would cause 23 million people to lose insurance. Trump had called the House bill “mean” and asked Senate Republicans to come up with “more generous” legislation.

Democrats uniformly oppose both the House and Senate versions of the bill.

“CBO’s report today makes clear that this bill is every bit as ‘mean as the House bill,” Senator Chuck Schumer (D-NY), the Democratic leader, told reporters.

In a statement on Monday, the White House criticized the CBO for issuing a “flawed report” and said its assessments should not be “trusted blindly.”