"It's very difficult for me to envision a scenario where I would end up voting for this bill," Collins told CNN's Jake Tapper on "State of The Union." "What I am doing, as is my general practice, is I would like to see the Congressional Budget Office analysis, which is expected to come out tomorrow morning."
Collins' vote is key. There are already two Republican senators on record opposing the bill from GOP Sens. Lindsey Graham of South Carolina and Bill Cassidy of Louisiana. One more Republican "no" vote and the legislation's future is all but over in the Senate, where Republicans only have until September 30 to overhaul the law with 51 votes, according to the Senate's parliamentarian.
Sen. John McCain, an Arizona Republican, declared his opposition to Graham-Cassidy on Friday afternoon citing concerns that the bill did not go through "regular order," a series of hearings, markups and an open-amendment process. Sen. Rand Paul, a Republican from Kentucky, has also been clear since Graham-Cassidy gained momentum last week that he is opposed to the legislation.
As she has done repeatedly in recent days, Collins was sharply critical of the bill Sunday, saying, "I have a number of very serious reservations about it."
"I'm concerned about the impact on cost and coverage," she said. "We already have a problem under the Affordable Care act with the cost of premiums and deductibles, and finally, I'm very concerned about the erosion of protections for people with pre-existing conditions."
Collins' comments were consistent with what she told reporters Friday that she was "leaning against" the bill, according to The Portland Press Herald
Collins' concerns over Graham-Cassidy have ranged across a host of issues, including the way the bill would end Obamacare subsidies and Medicaid expansion, and instead give states a set amount of funding through block grants. Collins has said that she fears Graham-Cassidy might also take away protections for people with pre-existing conditions if insurers in certain states are allowed to charge more based on a person's health history.
"I'm reading the fine print on Graham-Cassidy," Collins said, according to the Press Herald. "The premiums would be so high they would be unaffordable."
Republicans have been desperate to make one last push to repeal Obamacare, but so far signs point to a reality where the party may not be successful once again. On Friday, Vice President Mike Pence met with Maine's own governor, Paul LePage, in Washington to discuss the Republican agenda, but also to add pressure to Collins. There's little evidence it has made a difference.
"There is a lot of pressure, but I've had a lot of pressure on a lot of different issues over the years," Collins said Friday according to the Press Herald.
Senate Majority Leader Mitch McConnell said last week in a statement that it was his "intention" to consider Graham-Cassidy next week, but without the votes, it's unclear that Republican leaders would actually bring the bill to the floor. It could force members to go on the record on a bill that many are still learning about.
Eyes are also on Alaska Sen. Lisa Murkowski, another Republican who has yet to announce where she stands on Graham-Cassidy. As of Friday, Murkowksi's staff said the senator was undecided and planned to take the weekend to review the legislation. Over the weekend, her governor -- independent Bill Walker, whom Murkowski has recently said she relied on for guidance -- told The New York Times
that he saw no world in which Graham-Cassidy would be workable in the state.
"Alaska would fare very, very poorly," he said according to the Times. "Nothing has been brought to my attention that would increase my comfort level."
The Alaska Department of Health and Social Services also released a report Friday revealing its initial analysis projecting that over 10 years, Alaska would receive 65% less in federal funding under Graham-Cassidy.
McCain, Murkowski and Collins were the three Republican "no" votes who halted another attempt by GOP Senate leaders to repeal and replace Obamacare, the so-called "skinny repeal" bill, which lost in dramatic fashion during a late-night vote in July (Paul backed that legislation). That defeat had been seen by many as the end of a seven-year campaign pledge by many Republicans to repeal Obamacare.
But with next week's deadline looming, and a debt-ceiling and government funding fight that wrapped up more quickly than expected, Republicans -- including the President -- rallied around Graham-Cassidy last week, even though there was little evidence to suggest that any of the divisions that prevented the advancement of bills earlier this year had been remedied.
This story has been updated and will update with breaking news.