Sen. John McCain (R-Ariz.) announced on Friday that he will vote against the latest GOP effort to repeal ObamaCare, potentially dooming the legislation.

“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,” he said in a statement, referring to the legislation spearheaded by GOP Sens. Lindsey Graham (S.C) and Bill Cassidy (La.). 

McCain’s announcement leaves GOP leadership with no room for error. They need 50 GOP senators to support the legislation, and Sen. Rand Paul (R-Ky.) has already said he will vote no. Sen. Susan Collins (R-Maine) on Friday said she is leaning against the bill.