Republicans’ latest bid to roll back the Affordable Care Act appeared to collapse Monday as a third GOP senator came out against the measure and the Congressional Budget Office predicted major coverage losses should it become law.

Sen. Susan Collins, R-Maine, who voted against the last Republican repeal bill, joined Sens. John McCain, R-Ariz., and Rand Paul, R-Ky., in effect sealing the fate of the GOP effort. Republicans had hoped to rush through a sweeping repeal proposal this week over the objections of nearly every major organization representing patients, physicians, hospitals and others in the health care system.

"Part of the problem that we have had has been the lack of hearings debates and careful consideration and vetting of the health care replacement bills," Collins said.

With only 52 Republicans in the Senate and Democrats united in opposition, GOP leaders could afford to lose only two votes.

Collins’ announcement followed release of a preliminary analysis from the Congressional Budget Office of the Senate GOP plan, written by Sens. Lindsey Graham, R-S.C., and Bill Cassidy, R-La. It predicted "the number of people with comprehensive health insurance that covers high-cost medical events would be reduced by millions."

Monday afternoon, Senate Finance Committee Chairman Orrin G. Hatch, R-Utah, said GOP leaders would probably not be able to hold a vote this week on the plan.

And even before Collins’ announcement Monday, President Donald Trump sounded increasingly doubtful about the bill’s chances.

“We’re going to lose two or three votes, and that’s the end of that,” Trump said Monday on Alabama radio’s popular “Rick and Bubba Show,” criticizing Republican senators for withholding their support after years of promising to repeal and replace the law. “They pander and they grandstand.”

Plans for this week’s vote remain uncertain.

Meanwhile, protesters arrived in force at the Capitol, filling the hallways ahead of the one planned public hearing on the legislation.

Consumer advocates stepped up warnings that the bill would be devastating to sick Americans.

“This bill is an even harsher version of the previous failed proposals that were overwhelmingly rejected by Americans,” said Betsy Imholz, special projects director for Consumers Union. “It is not only a repeal of the Affordable Care Act — threatening key consumer protections and coverage requirements that ensure those with preexisting conditions have access to meaningful care — but also a historic undercutting of the Medicaid program.”

Cassidy and Graham have said Americans will not lose vital insurance protections, including the guarantee that they could get insurance even if they are sick.

“This plan protects those with preexisting conditions and gives states resources and flexibility to lower premiums and increase the number of Americans insured,” Cassidy said Monday after releasing his latest proposal.

But those claims have been refuted by nearly every major voice in the U.S. health care system, including leading hospitals, physician groups and patient advocates.

On Monday, 36 current and former state insurance commissioners, including several Republicans, sent a strongly worded letter to congressional leaders urging them to reject the latest proposal.

“The Cassidy-Graham bill would increase the number of people without health coverage and severely disrupt states’ individual insurance markets, with sharp premium increases and insurer exits likely to occur in the short term and over time,” wrote the commissioners.

Senate Republican leaders and the Trump administration were trying to woo key Republican senators who have expressed strong doubts about the bill.

Collins had already hinted in an interview on CNN on Sunday that “it’s very difficult for me to envision a scenario where I would end up voting for this bill.”

On the right, Paul, who has previously said several times that he opposes the bill, kept up his criticism Monday. He remains opposed, a spokesman said. And Sen. Ted Cruz, speaking in his home state of Texas, said that "right now they don't have my vote." He, too, remained unmoved Monday. Cruz said he did not think Sen. Mike Lee, R-Utah, was supporting the bill either, though Lee’s office said Monday that the senator was reviewing the latest version.

Sen. Lisa Murkowski of Alaska, who opposed the last GOP repeal effort, has said she remains undecided.

The revised version would send more money to Alaska, Arizona and Maine in a clear effort to win over Murkowski, McCain and Collins.

And in a bid to win over Cruz and other conservatives, Graham and Cassidy appear to have further weakened consumer protections, giving states more authority to waive requirements such as the prohibition on insurers charging sick people more for coverage.

The full impact of the changes will be difficult to assess as the nonpartisan Congressional Budget Office, which lawmakers rely on to analyze major legislation, will not have time to issue a full report on the new proposal.

Senate Republicans must vote this week before a Sept. 30 deadline, after which they can no longer use a special rule that allows them to advance repeal legislation with only 50 votes instead of the 60 normally required to pass controversial bills in the Senate.

That would require them to vote on one of the most sweeping pieces of domestic legislation in at least half a century with almost no time for study and debate.

House Republicans have indicated they are in no such rush, not guided by Senate rules, and would not likely vote until skeptical lawmakers — especially those Republicans in California, New York and other states that would lose health care funding — could review the Senate legislation.

The GOP proposal would not only roll back the government programs created by the current law to guarantee Americans’ health coverage, it would completely restructure the 52-year-old system of federal support for state Medicaid programs that currently cover approximately 70 million people.

It would also dramatically cut future Medicaid funding that supports coverage for poor children, mothers, seniors and the disabled.

At the same time, the bill would give states broad new authority to remake their healthcare systems and waive many protections in the current law.

lisa.mascaro@latimes.com

@LisaMascaro