Story highlights Republicans are trying to pass a health care bill before an end-of-the-month deadline

With two GOP senators against the current proposal, just one more stops the bill

(CNN) Sen. Susan Collins said Sunday morning that it would be "very difficult for me to envision a scenario" where she would vote for Republicans' latest plan to repeal and replace Obamacare, but the Maine Republican said she wanted to wait for a Congressional Budget Office score of the Graham-Cassidy bill before rendering a final decision.

"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."

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