By MJ Lee and Tami Luhby CNN

(CNN) -- Fourteen million more Americans would be uninsured under the House Republican health care bill than under Obamacare in 2018, rising to 24 million by 2026, the non-partisan Congressional Budget Office said Monday.

The long-anticipated score immediately puts the writers and supporters of the GOP Obamacare bill on the defensive. It is also certain to complicate the party's already troubled efforts to repeal and replace the Affordable Care Act.

The CBO, along with the Joint Committee on Taxation, found that 5 million fewer people would be covered under Medicaid by 2018, and 14 million fewer people would enroll in the program by 2026. Meanwhile, 6 million fewer Americans would be covered in the individual market by 2018, but by 2026, only 2 million fewer people are expected to be covered. That's in part because fewer employers would offer insurance to their workers, driving more people to the individual market.

In total, an estimated 52 million people would be uninsured by 2026 under the GOP plan, compared to 28 million who would lack insurance under the current law.

The Republican bill, titled the American Health Care Act, would reduce the federal deficits by $337 billion over 10 years, the CBO said.

The legislation, introduced last Monday, has sparked deep concern among Republican lawmakers in both the House and the Senate. The sources of unease are wide-ranging.

Prominent conservatives on Capitol Hill, for example, have argued that the bill doesn't go far enough, labeling it "Obamacare Lite." One element of the legislation that has drawn fierce scorn is the refundable tax credits, which conservative Republicans say amounts to an entitlement program.

Moderate Republicans are also uneasy, particularly when it comes to the proposal's impact on Medicaid expansion. Thirty-one states -- including 16 with Republican governors -- elected to expand Medicaid under Obamacare and have found it to be a successful way of insuring low-income adults at little cost to their states.

The House GOP bill proposes scrapping the enhanced federal funding for Medicaid expansion in 2020 and overhauls the entire program so that states receive a fixed amount of money per enrollee.

Republicans downplaying the report

In the lead up to the CBO score, Republicans have preemptively downplayed its significance.

"The one thing I'm certain will happen is CBO will say, 'Well, gosh, not as many people will get coverage.' You know why? Because this isn't a government mandate," House Speaker Paul Ryan said on CBS over the weekend. "So there's no way we can compete with, on paper, a government mandate with coverage."

More important than the CBO's prediction of how many people would be covered under the bill, Ryan added, is the goal of lowering the cost of care by expanding choice and competition.

One House GOP aide put it this way: "They're saying people are losing coverage but in reality, these people are making a choice," the aide said. "We're not ripping coverage away."

White House spokesman Sean Spicer even went as far as to question the group's accuracy.

"If you're looking to the CBO for accuracy, you're looking in the wrong place," Spicer told reporters last week.

Republican backers of the bill are also stressing that the CBO score won't take into account the effects of other healthcare reforms that Republicans hope to enact, including through legislation and administrative actions from Health and Human Services Secretary Tom Price.

One particular promise from Price could soon haunt Republicans.

"I firmly believe that nobody will be worse off financially in the process that we're going through," Price said on NBC's "Meet the Press" Sunday.

Doug Elmendorf, former director of the Congressional Budget Office, said on CNN on Monday that Price's claim was "absurd."

"This legislation will cut subsidies substantially; millions of people will lose health insurance," Elmendorf said. "But certainly people will be worse off."

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