But the budget office put Republicans in an untenable position. It found that next year, 15 million more people would be uninsured compared with current law. Premiums and out-of-pocket expenses could shoot skyward for some low-income people and for people nearing retirement, it said.
The legislation would decrease federal deficits by a total of $321 billion over a decade, the budget office said.
Mr. McConnell, the chief author of the bill, wanted the Senate to approve it before a planned recess for the Fourth of July, but that looks increasingly doubtful. Misgivings in the Republican conference extend beyond just a few of the most moderate and conservative members, and Mr. McConnell can lose only two Republicans.
At least some of Ms. Collins’s concerns could be shared by Senators Lisa Murkowski of Alaska and Shelley Moore Capito of West Virginia, whose rural states would face effects similar to those in Maine.
“If you were on the fence, you were looking at this as a political vote, this C.B.O. score didn’t help you,” said Senator Lindsey Graham, Republican of South Carolina. “So I think it’s going to be harder to get to 50, not easier.”
He added, “I don’t know, if you delayed it for six weeks, if anything changes.”
Under the bill, the budget office said, subsidies to help people buy health insurance would be “substantially smaller than under current law.” And deductibles would, in many cases, be higher. Starting in 2020, the budget office said, premiums and deductibles would be so onerous that “few low-income people would purchase any plan.”
Moreover, the report said, premiums for older people would be much higher under…