WASHINGTON — Sen. John McCain, R-Ariz., dealt a critical blow to Republicans’ last-ditch attempt to roll back the Affordable Care Act on Friday, announcing that he will not vote for repeal legislation that GOP leaders plan to bring to the Senate floor for a vote next week.

“We should not be content to pass health care legislation on a party-line basis,” McCain said in a lengthy statement criticizing the GOP rush to pass a repeal bill with only one scheduled hearing and little public scrutiny.

“I cannot in good conscience vote for the Graham-Cassidy proposal,” he said, referring to the repeal bill authored by Sens. Lindsey Graham, R-S.C., and Bill Cassidy, R-La.

McCain’s move raises serious questions about whether Republicans have the votes to advance their latest repeal effort, which only days ago seemed to be gaining considerable momentum.

The party, which has 52 votes in the Senate, can lose only two, or the bill will fail. Sen. Rand Paul, R-Ky., has already said he would oppose the bill, which he said maintains too much of the current law’s government spending on health care.

Sen. Susan Collins, R-Maine, a centrist Republican who helped sink the GOP repeal effort in July, has signaled strong reservations about the current proposal.

McCain also opposed that previous effort, casting a dramatic middle-of-the-night vote against the measure and calling for his colleagues to stop rushing through major health care legislation.

McCain reiterated those calls Friday. “As I have repeatedly stressed, health care reform legislation ought to be the product of regular order in the Senate. Committees of jurisdiction should mark up legislation with input from all committee members, and send their bill to the floor for debate and amendment,” the veteran lawmaker said.

“That is the only way we might achieve bipartisan consensus on lasting reform, without which a policy that affects one-fifth of our economy and every single American family will be subject to reversal with every change of administration and congressional majority.”

Senate Majority Leader Mitch McConnell, R-Ky., had indicated that he wanted to put the Graham-Cassidy proposal to a vote next week, as Republicans face a Sept. 30 deadline under Senate rules to be able to advance a repeal bill with only 50 votes.

The deadline, which was set through a process known as budget reconciliation, has prompted a roller-coaster scramble by Senate Republican leaders and the White House to round up the votes to revive their push.

President Donald Trump and Vice President Mike Pence have been calling senators for days trying to build support. GOP leaders have been offering various sweeteners to win votes, including more money for states such as Alaska.

Alaska Republican Sen. Lisa Murkowski cast the third vote against the last repeal push in July, joining Collins and McCain, and she has voiced concerns about the latest effort.

The proposal generated a storm of opposition in recent days from patient advocates, hospitals, physician groups and health care experts.