The Republican Party's last-ditch effort to repeal the Affordable Care Act was dealt a major blow Friday when Sen. John McCain (R-Ariz.) announced that he "cannot in good conscience vote for the Graham-Cassidy proposal," which analysts have called the most "brutal and deadly" version of Trumpcare yet.

Senate Majority Leader Mitch McConnell (R-Ky.) is expected to bring the legislation to the floor for a vote before the end of next week.

Physicians and public health researchers Drs. Steffie Woolhandler and David Himmelstein estimated in an analysis released Friday that, if passed, the Graham-Cassidy repeal bill could kill tens of thousands of people per year.

"The Graham-Cassidy bill—what we're calling 'The Undertaker Full Employment Act'—would cut health coverage by 14 million Americans in 2020, rising to at least 32 million in 2027," Dr. Woolhandler said in a statement. "That means 18,200 extra deaths in the first year, climbing to 41,600 annually within a decade."

Read McCain's full statement:

As I have repeatedly stressed, healthcare reform legislation ought to be the product of regular order in the Senate. Committees of jurisdiction should mark up legislation with input from all committee members, and send their bill to the floor for debate and amendment. That is the only way we might achieve bipartisan consensus on lasting reform, without which a policy that affects one-fifth of our economy and every single American family will be subject to reversal with every change of administration and congressional majority. I would consider supporting legislation similar to that offered by my friends Senators Graham and Cassidy were it the product of extensive hearings, debate and amendment. But that has not been the case. Instead, the specter of September 30th budget reconciliation deadline has hung over this entire process. We should not be content to pass health care legislation on a party-line basis, as Democrats did when they rammed Obamacare through Congress in 2009. If we do so, our success could be as short-lived as theirs when the political winds shift, as they regularly do. The issue is too important, and too many lives are at risk, for us to leave the American people guessing from one election to the next whether and how they will acquire health insurance. A bill of this impact requires a bipartisan approach. Senators Alexander and Murray have been negotiating in good faith to fix some of the problems with Obamacare. But I fear that the prospect of one last attempt at a strictly Republican bill has left the impression that their efforts cannot succeed. I hope they will resume their work should this last attempt at a partisan solution fail. I cannot in good conscience vote for the Graham-Cassidy proposal. I believe we could do better working together, Republicans and Democrats, and have not yet really tried. Nor could I support it without knowing how much it will cost, how it will effect insurance premiums, and how many people will be helped or hurt by it. 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. I take no pleasure in announcing my opposition. Far from it. The bill's authors are my dear friends, and I think the world of them. I know they are acting consistently with their beliefs and sense of what is best for the country. So am I.

I hope that in the months ahead, we can join with colleagues on both sides of the aisle to arrive at a compromise solution that is acceptable to most of us, and serves the interests of Americans as best we can.

Correction: An earlier version of this article misstated the estimated number of deaths that could result from the Graham-Cassidy legislation. It's actually higher than indicated, but was not stated properly.