With the Arizona senator's defection, there are now two declared GOP "no" votes on the repeal legislation, the other being Rand Paul of Kentucky.
McCain's chief complaint has been that the Republican-led effort to repeal Obamacare did not go through normal hearings, debate and amendment process that the Senate calls for.
In Maine, Collins said there are lots of numbers floating around, and she's awaiting an analysis by the Congressional Budget Office before she makes a final decision.
The latest bill was introduced by Republican Senators Bill Cassidy and Lindsey Graham, who is a close friend of McCain's. Collins and Sen. Lisa Murkowski (R-Alaska) have voiced such concerns.
In a series of tweets, Paul contended the Graham-Cassidy bill does not fulfill the Republican Party's longterm propose to totally ax Obama-era healthcare legislation.
Still, the White House isn't expected to lay off.
To make a September 30 deadline, Republican senators meant to bring the bill offered by Sens. He said all the bill does is set up a "perpetual food fight" over how that money is distributed to states. GOP leaders are also expected to unveil their most detailed blueprint yet of the tax reform plan they hope to pass by the end of the year.
"It's very hard for me to envision a scenario where I end up voting for this bill", Collins said Sunday on CNN's "State of the Union". That all but ensured a major setback for President Donald Trump and Senate Majority Leader Mitch McConnell, and appeared likely to deepen rifts between congressional Republicans and a president who has begun making deals with Democrats out of frustration with his own party's failure to turn proposals into laws.
A third Republican "no" vote sank a different version of Obamacare repeal in July.
The bill has been roundly rejected by influential national groups representing physicians, hospitals and insurers.
"While we sometimes disagree on important issues in health care, we are in total agreement that Americans deserve a stable healthcare market that provides access to high-quality care and affordable coverage for all", the statement reads.
The other swing votes are Sens.
Sean Spicer on his surprise Emmys appearance
The image flashed up on the screen and he joked, "These Hollywood phonies kissing up to Sean Spicer are disgusting". I'm not one of these people who has a couple of drinks and goes around kissing people that I don't know.
"Without a full CBO score, which won't be available by the end of the month, we won't have reliable answers to any of those questions", said McCain.
The senator said she had a lengthy chat with Vice President Mike Pence on Saturday.
"I'm not going to trade my vote for something ancillary or be bribed", Paul said. "So it may be hard for the CBO to do the kind of in-depth analysis that it usually does, but that's what I would like to see before making a formal decision".
"Nor could I support it without knowing how much it will cost, how it will affect insurance premiums, and how many people will be helped or hurt by it".
Ducey also asserts that "51 votes are still possible", a reference to the number of "yes" votes needed for Senate approval.
"They're pleasant conversations", Paul said.
The tweet echoes his remarks from last night's rally in Alabama, where the President stated, "I haven't given up on him, because I think he may come around".
"Right now, they don't have my vote", Cruz said at a festival in Austin, Texas.
But Paul cracked the door open to providing some funds to states if the amount of money was significantly reduced from the levels under Cassidy-Graham.
Arizona Gov. Doug Ducey came out in support of Graham-Cassidy on Monday, saying in a statement it "is the best path forward to repeal and replace Obamacare". "I'm very excited about it, we've finally found an alternative to ObamaCare".
The Louisiana Republican sponsored the legislation with South Carolina GOP Sen.