“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 the Senate bill than under current law. As an example, it said, for a typical 64-year-old with an annual income of $26,500, the net premium in 2026 for a midlevel silver plan, after subsidies, would average $6,500, compared with $1,700 under the Affordable Care Act. And the insurance would cover less of the consumer’s medical costs.

Likewise, the report said, for a 64-year-old with an annual income of $56,800, the premium in 2026 would average $20,500 a year, or three times the amount expected under the Affordable Care Act.

The budget office report was a major setback to Senate Republican leaders, but it was too early to declare the legislation dead, and turmoil in health insurance markets could still induce Congress to take action this year. Many people thought the House repeal bill was dead after Speaker Paul D. Ryan pulled it from the floor on March 24, but a slightly revised version was narrowly approved by the House six weeks later.

Senator John Thune of South Dakota, a member of the Republican leadership, suggested that leaders would press forward with the Senate bill. He said that an argument could be made for delaying it “if you thought you were going to get a better policy,” but that that was not the case.