WASHINGTON — Sen. Susan Collins of Maine, a key Republican vote on health care, announced Monday that she will oppose the last-ditch GOP effort to overhaul Obamacare, essentially leaving the bill dead.

Republicans, with 52 seats in the Senate, can lose just two votes and still pass the bill introduced by Sens. Lindsey Graham, R-S.C., Bill Cassidy, R-La., Dean Heller, R-Nev., and Ron Johnson, R-Wis.

Majority Leader Mitch McConnell, R-Ky., intended to bring the bill to the floor for a vote this week before a Sept. 30 deadline for the Senate to act.

Republican Sens. John McCain of Arizona, Rand Paul of Kentucky and Ted Cruz of Texas have all said they are against the bill. While Cruz had been against the current version, he had been hoping for more tweaks in the legislation. Shortly after Collins' announcement, Cruz tweeted: "We cannot give up on Obamacare repeal. We must keep working. We can get to yes."

However, the bill’s sponsors already made changes over the weekend to the funding model in the hopes of winning some votes.

Collins’ announcement came just after after the nonpartisan Congressional Budget Office released a limited analysis estimating “the number of people with comprehensive health insurance that covers high-cost medical events would be reduced by millions" under the legislation over the next decade. CBO said it was not clear the exact number of people who would be uninsured because it was difficult to estimate how states would react.

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If passed, the legislation would have kept most of the Obamacare taxes in place but sent the money back to the states in the form of block grants to design their own health systems, waiving Obamacare's minimum insurance requirements. It would have also ended the Affordable Care Act's expansion of Medicaid eligibility and temporarily replaced that money with block grants through 2026.

The bill would also overhaul the traditional Medicaid program and replace it with a per-capita grant program. Collins said the bill's changes to Medicaid would "have a devastating impact."

Collins also said she had issues with the Graham-Cassidy waiver system, which she said would "weaken protections for people with pre-existing conditions."

“The CBO’s analysis on the earlier version of the bill, incomplete though it is due to time constraints, confirms that this bill will have a substantially negative impact on the number of people covered by insurance," Collins said in a statement.

Collins said she had no confidence that the new version of the bill released over the weekend would improve the legislation or dampen its negative impact on Maine. "This is simply not the way that we should be approaching an important and complex issue that must be handled thoughtfully and fairly for all Americans," she said.

The CBO also estimated "disruptions and other implementation problems would accompany the transition" because of the short time frame that states would have to set up their health systems.

Collins said she had been lobbied by President Trump, Vice President Pence and others. "It would probably be a shorter list of who hasn't called me on this bill," she told reporters.

The Maine senator is a member of the Senate Health, Education, Labor and Pensions Committee, which had been working on a bipartisan approach to stabilize the individual health insurance market until last week, when Chairman Lamar Alexander, R-Tenn., announced he was unable to come to a compromise with the committee's top Democrat.

Collins told reporters Monday evening she was encouraged by the bipartisan process on the Senate HELP Committee. She said the focus should be on fixing Obamacare rather than replacing it.

"Once this bill goes down, (HELP Committee) negotiations should pick up right where they left off. There’s no time to waste," Senate Minority Leader Chuck Schumer, D-N.Y., said Monday night, citing Collins' recent opposition.

Her announcement followed a Finance Committee hearing on the legislation that took up much of the afternoon — including a brief delay caused by protesters, many in wheelchairs, chanting their opposition to Medicaid cuts.

The hearing had been an attempt to appease lawmakers who had been critical of the lack of regular order that had gone on with the bill, but following the weekend's announcements of opposition by key senators, it seemed like merely a formality.

During a recess in the hearing, Finance Chairman Orrin Hatch, R-Utah, was asked by a reporter what chance the bill has of passing. “Zero," he replied. "I don’t think it has much chance. The Democrats aren’t going to support it. They’re too interested in demagoguing it.”