Sen. John McCain (R-AZ) issued a lengthy statement Friday afternoon announcing his opposition to the last-ditch Obamacare repeal effort in the Senate, which GOP leaders were hoping to bring for a vote next week.

“I cannot in good conscience vote for the Graham-Cassidy proposal,” McCain said in the statement, referring to the bill Republicans were planning to put on the floor.

His opposition is a major setback, if not full-on death sentence, for the legislation. Senate Republicans can only lose two GOP votes and still pass the bill. Sens. Rand Paul (R-KY) and Susan Collins (R-ME) have also signaled they’re very likely to vote against the bill. The deadline for the Senate to move forward on the Obamacare repeal effort that passed out of the House is Sept. 30.

McCain was the key vote that torpedoed Senate Republicans’ last Obamacare repeal effort in July, with a late-night surprise vote against a previous proposal that would have gone to a conference committee between the House and the Senate. That dramatic vote came after McCain was rushed back to Washington from Arizona, where he has been receiving cancer treatments. McCain had voted in favor of advancing an Obamacare repeal bill in an initial procedural vote, but then gave a riveting speech on the Senate floor ripping lawmakers for abandoning the traditional legislative process.

Likewise, the statement McCain issued Friday focused on the process complaints about the latest bill, sponsored by Sen. Bill Cassidy (R-LA) and McCain’s good friend, Sen. Lindsey Graham (R-SC). Their bill was only introduced earlier this month, and Republicans intended to vote on it next week with only a preliminary Congressional Budget Office score that would not have analyzed the legislation’s effects on health care coverage or its overall costs to the federal government.

If Senate Republicans do not pass a repeal bill out of their chamber by Sept. 30, they will have wasted the legislative vehicle they were using to avoid a Democratic filibuster.

Graham said on Twitter that he “respectfully disagree[d]” with McCain’s decision, but said that their friendship was “not based on how he votes but respect for how he’s lived his life and the person he is.”

“I’m excited about solutions we have found in Graham-Cassidy-Heller-Johnson. We press on,” Graham continued.

Cassidy’s response to McCain’s opposition was more curt:

“I am disappointed that Senator John McCain is not voting to repeal and replace Obamacare. But, as long as there are families being penalized because they can’t afford insurance costing $30,000 to $40,000 a year, I will continue to work for those families,” he said in statement.

Sen. John Thune (R-SD), a member of the Senate GOP leadership team, said on Fox News that losing McCain’s support was “certainly not a good development for passage of the bill.” He was hopeful, however, that there was “an opportunity between now and September 30th, the end of next week, to get a vote on this, an affirmative vote.”

McCain on Friday called for the Senate to get back to the bipartisan negotiations on a more limited Obamacare fix, that had been called off by Republicans as they hoped to push through the Graham-Cassidy repeal.

“I believe we could do better working together, Republicans and Democrats, and have not yet really tried,” McCain said. “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.”