Senate Republicans’ bill to erase major parts of the Affordable Care Act would cause an estimated 22 million more Americans to be uninsured by the end of the coming decade — only about a million fewer than similar legislation recently passed by the House, according to the Congressional Budget Office.

The forecast issued Monday by Congress’s nonpartisan budget scorekeepers also estimates that the Senate measure, drafted in secret mainly by Majority Leader Mitch McConnell and aides, would reduce federal spending by $321 billion by 2026 — compared with $119 billion for the House’s version.

The CBO estimates that two-thirds of the drop in health coverage a decade from now would fall on low-income people who rely on Medicaid. And among the millions now buying private health plans through ACA marketplaces, the biggest losers would roughly parallel the ones under the House’s legislation: The sharpest spike in insurance premiums would fall on middle-aged and somewhat older Americans.

The CBO’s analysis has been awaited as a crucial piece of evidence as McConnell (Ky.) and other Republican leaders try to hurry a vote on the bill this week. They have been navigating an expanding minefield of resistance from their own party’s moderate and conservative wings, while Democrats are united against the measure.

The release of the 49-page report late Monday afternoon seemed to worsen the bill’s prospects. No new senators immediately said they would back the legislation, and at least three wavering members of the GOP caucus said they would vote against starting debate Tuesday on the bill in its current form. A fourth, Sen. Dean Heller (R-Nev.), had expressed his opposition last week.

The Senate bill could undergo further changes before such a vote is scheduled, which could prompt these senators to reconsider. If the Democrats vote as a bloc, McConnell can afford to lose no more two Republican votes for a procedural motion to succeed.

Asked whether McConnell and other Senate leaders had amassed enough support to pass the measure, Sen. Roy Blunt (R-Mo.) responded, “Anyone would tell you they don’t.”

Early in the evening, Sen. Susan Collins (R-Maine) tweeted that she would not agree to proceed on Tuesday. The measure would “hurt most vulnerable Americans” and failed to solve the problems of access to care in rural Maine where, she wrote, “hospitals are already struggling.”

Meanwhile, conservative Sen. Rand Paul (R-Ky.) labeled the Better Care Reconciliation Act “a terrible bill” and repeated his contention that it would not go far enough in repealing the sprawling health-care law enacted seven years ago by a Democratic Congress and president.

McConnell took to the Senate floor just before the report’s release to press anew for rapid action. He made it clear that the bill, already tweaked early Monday, could be negotiated further to try to win over holdouts.

“The American people need better care right now,” McConnell said. “This legislation includes the necessary tools to provide it.”

See where the Senate health-care bill’s subsidy cuts will affect Americans most

Democrats quickly seized on the CBO’s projection of how much the ranks of the uninsured would grow. “No matter how the…