Mr. McConnell already faced a host of reservations from across the ideological spectrum in his conference. Five Republican senators have said they cannot support the version of the bill that was released last week, and Mr. McConnell can afford to lose only two.
Before the budget office released its report on Monday, the American Medical Association officially announced its opposition to the bill, and the National Governors Association urged the Senate to slow down.
Now, the budget officeâs findings will give fodder to Democrats who were already assailing the bill as cruel. It could give pause to some Republican senators who have been mulling whether to support the bill â or it could give them an additional reason to come out against the bill altogether.
It is still unclear whether the new budget office projections will be judged against the Houseâs version, or against the Affordable Care Actâs coverage figures. Beyond the number of Americans without health insurance, the Senate billâs $321 billion in deficit reduction is larger than the $119 billion total that the budget office found for the bill that passed the House.
Earlier Monday afternoon, Senate Republican leaders altered their health bill to penalize people who go without health insurance by requiring them to wait six months before their coverage would begin. Insurers would generally be required to impose the waiting period on people who lacked coverage for more than about two months in the prior year.
The waiting-period proposal is meant to address a conspicuous omission in the Senateâs bill: The measure would end the Affordable Care Actâs mandate that nearly all Americans have health insurance, but it also would require insurers to accept anyone who applies. The waiting period is supposed to prevent people from waiting until they get sick to purchase a health plan. Insurers need large numbers of healthy people to help pay for those who are sick.
Under one of the most unpopular provisions of the Affordable Care Act, the government can impose tax penalties on people who go without health coverage. Republicans have denounced this as government coercion.
The repeal bill passed by the House last month has a different kind of incentive. It would impose a 30 percent surcharge on premiums for people who have gone without insurance. But the Congressional Budget Office said this provision could backfire. As a result of the surcharge, it said, two million fewer people would enroll, and the people most likely to be deterred would be those who are healthy.
The Senate proposal for a waiting period could also have problems. For someone with cancer or a severe illness, a six-month waiting period could be a death sentence.
âBeing denied critical and potentially lifesaving health care for six months is not a fair punishment for someone who is a few hundred dollars short on insurance payments because they lost their job and finances are unexpectedly tight,â said Senator Chuck Schumer of New York, the Democratic leader.
In yet another rebuke from outside Congress, the A.M.A., the nationâs largest physicians organization, declared on Monday, âMedicine has long operated under the precept of primum non nocere, or âfirst, do no harm.â The draft legislation violates that standard on many levels.â
The insurer Anthem, on the other hand, offered some positive words about the bill, saying in a statement that it believed the Senate legislation would âmarkedly improve the stability of the individual market.â
Senate Republican leaders were also facing increased pressure to delay the vote so that lawmakers, governors and consumers could investigate the likely effects of the legislation.
One of the five Republicans who said they would not vote for the bill that was released last week, Ron Johnson of Wisconsin, argued against holding a vote this week.
âI see what leadershipâs trying to do,â he told the radio host Hugh Hewitt. âTheyâre trying to jam this thing through.â Mr. Johnson added, âAll Iâm asking is letâs give ourselves a few more days. Maybe a week or two.â
Top Republicans showed no signs of yielding to the pressure.
The No. 2 Senate Republican, John Cornyn of Texas, had previously left the door open to voting on the bill sometime in July. But on Monday he wrote on Twitter: âI am closing the door. We need to do it this week before double digit premium increases are announced for next year.â
President Trump struck a tone of resignation Monday on Twitter, noting that Republican senators were working hard to pass their repeal bill.
âNot easy! Perhaps just let OCare crash & burn!â Mr. Trump wrote, reiterating his assertion that President Barack Obamaâs signature health care law will be doomed if Congress does not come to its rescue.
Though Senate Republicans vowed to write their own bill after the House passed its repeal bill last month, the legislation released by the Senate last week is broadly similar.
The Senate bill would end the requirement that most Americans have health coverage while setting up a revamped system of tax credits to help people buy insurance on the individual market. It would repeal most of the taxes imposed by the Affordable Care Act, including those on high-income people and on health care companies.
The measure proposed in the Senate would also make sweeping changes to Medicaid, the federal-state health program for low-income people, which would have major implications for states in the long term. The bill would roll back the expansion of Medicaid under the Affordable Care Act, and it would change the broader Medicaid program from an open-ended entitlement to a program with capped payments to states.