Washington: US Senator John McCain Friday announced his opposition to the latest Republican attempt to replace Barack Obama’s signature health care law, likely dooming the repeal effort.

It is the second time in two months that he has defied his party and President Donald Trump over efforts to replace the Affordable Care Act, often referred to as “Obamacare,” which has long been in Republicans’ sights.

“I cannot in good conscience vote for the Graham-Cassidy proposal,” McCain said of the bill proposed by fellow Republican senators Lindsey Graham and Bill Cassidy.

“I believe we could do better working together, Republicans and Democrats, and have not yet really tried,” the senator said in a statement.

In July, McCain made a dramatic return to Washington from Arizona after a brain cancer diagnosis to become one of three Republican senators who helped sink their party’s earlier bid to replace Obamacare.

Now, rebels within the party ranks appear set to torpedo what may be the party’s last chance to make good on a longstanding Republican goal, and a signature pledge of the president.

With both McCain and the conservative Rand Paul opposed, it would take just one more Republican defector to prevent the bill’s passage before a deadline of September 30, the end of the fiscal year. At least two party moderates — Susan Collins and Lisa Murkowski — are known to have serious reservations.

The bill’s collapse would be yet another blow to the president and the Republican leadership, who have been unable to move forward on repealing Obamacare despite controlling Congress and the White House.

In coming out against the latest bill, McCain criticized the fact that it had bypassed regular Senate order, and noted that it would not be fully reviewed by the non-partisan Congressional Budget Office (CBO) before the end of the month.

The senator said he could not “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.”

Trump targets defectors

The bill’s supporters might be eager to avoid a CBO score. In July, the non-partisan body projected that the ranks of the uninsured would grow by 23 million Americans, and premiums would rise 20 percent annually, over the next decade if the previous Obamacare repeal bill became law.

The White House scrambled earlier this week to win over Republicans skeptical of Graham-Cassidy, with Trump himself phoning lawmakers and state governors seeking to tilt the scales in favor of the bill.

And Trump made his position on Republican defectors clear on Friday, writing on Twitter that those who vote against Graham-Cassidy “will forever…. be known as ‘the Republican who saved Obamacare.'”