Senator John McCain (R-AZ) announced his opposition to the Graham-Cassidy legislation on Friday, likely killing the bill’s chances of passing in the Senate.

“I cannot in good conscience vote for the Graham-Cassidy proposal,” McCain said in a statement. “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 affect 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.”

McCain acknowledged that it was a tough decision for him given his personal relationship with Senator Lindsey Graham (R-S.C.), one of the bill’s co-authors.

“I take no pleasure in announcing my opposition,” McCain wrote. “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.”

Graham, for his part, responded in a tweet saying that the difference in opinion would not damage the personal relationship.

"My friendship with @SenJohnMcCain is not based on how he votes but respect for how he’s lived his life and the person he is," he wrote.

The Arizona Senator had dramatically killed the Republican Party’s last attempt to pass an Obamacare repeal and replace bill, when he walked into the chamber and gave a thumbs-down signal to oppose the so-called “skinny repeal” proposal.

Since then he has been targeted repeatedly by President Donald Trump for being the one vote in the way of the party achieving a seven-year long promise to upend the Affordable Care Act.

But McCain, who is currently fighting brain cancer, has insisted that he wants any health care bill to be considered through regular order—which involves committee hearings and the opportunity to propose and consider amendments. Graham-Cassidy was rushed to consideration during the past week because the Republican Party has a September 30th deadline by which they can pass health care legislation by a simple majority vote.

Without McCain’s backing it is highly unlikely that they will be able to muster 50 votes. Already, Senator Susan Collins (R-ME) has indicated that she is "leaning against the bill" and Senator Rand Paul (R-KY) has said that he will oppose the measure. With McCain saying he will too, that leaves just 49 Republican Senators in support.

Senate Minority Leader Chuck Schumer (D-NY) praised McCain's decision in a statement. “John McCain shows the same courage in Congress that he showed when he was a naval aviator," Schumer wrote. "I have assured Senator McCain that as soon as repeal is off the table, we Democrats are intent on resuming the bipartisan process.”