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But if the Republican-controlled Senate holds its current plan, which would repeal most of the law and allow states to decide their own health care policies and to expand Medicaid, many Americans who work full time won’t be able to afford the premiums in some plans.

Many Americans who sign up for coverage on new exchanges would also face steep fees to get coverage in the marketplaces and then pay a penalty.

Under the Senate plan, about 800,000 people who were losing their coverage under the Affordable Care Act could keep it under the new system.

Some Republicans would like to make it easier for insurers to sell insurance plans across state lines and have Congress revise the 2010 law so that Congress could have a greater role in setting insurance rates. However, Republicans believe that any effort to roll back the law’s subsidies will also be used to undermine the law.

Congressional Republicans like Senator Lamar Alexander, the majority leader, said the legislation would keep coverage stable and provide states more flexibility. Under the legislation, the federal government would be permitted to let the states set up a pool of people who may qualify for low-cost plans while taking a larger portion of federal money.

Under the Senate bill, the federal government would stop the cost-policymaking for state insurance agencies, which was put in place under Congress’ 2010 law. It would instead leave decision-making to each state.

The nonpartisan Congressional Budget Office said Thursday that the Senate bill would leave 12 million more Americans without health coverage. CBO estimated that some 8 million fewer people would have insurance.

Senator Patty Murray, the ranking Democrat on the Senate health committee, said that the bill left people with high-cost, high-quantity plans.

While Republicans have touted their proposal as an Obamacare repeal, the bill has plenty of Republican supporters, including people who say they will gain more coverage than those people losing it.

In Colorado, where Republicans are trying to take on the Democratic state government, the governor has refused to commit, saying he will wait till the Senate bill is written before deciding on whether to sign on to the plan.