U.S. Sen. John McCain was the center of attention -- and scrutiny -- on Capitol Hill on Friday morning after the "skinny repeal" amendment, part of Senate Republicans' plan to repeal ObamaCare, was defeated in a 51-49 vote.

The Arizona Republican’s “no” vote shortly after 1:30 a.m. ET sent audible gasps throughout the Senate chamber, ruining Republicans hopes of a 50-50 vote and a tiebreaker by Vice President Mike Pence.

Just days ago, McCain had voted "yes" on a procedural measure that led to Friday morning's vote, sparking confidence among some Republicans that there was a chance McCain would back the "skinny repeal" amendment as well.

But after the amendment failed, Senate Majority Leader Mitch McConnell voiced his frustrations: “This is clearly a disappointing moment,” McConnell said. “I regret that our efforts were simply not enough — this time.”

Following the vote, protesters were heard outside the Capitol chanting, “Thank you, John McCain!”

Prior to the vote, Senate Republicans, including McConnell and Pence, were seen trying to convince McCain to support the amendment, but the famed Senate "maverick" stuck to his “no” vote.

McCain’s office released a statement immediately following the vote.

"From the beginning, I have believed that ObamaCare should be repealed and replaced with a solution that increases competition, lowers costs, and improves care for the American people,” he said. “The so-called 'skinny repeal' amendment the Senate voted on today would not accomplish those goals.”

McCain returned to Washington on Tuesday for the health care proposal, nearly a week after announcing he had been diagnosed with an extremely rare form of brain cancer and undergone surgery above his left eye.

The other two Republican senators to vote “no” were Susan Collins of Maine and Lisa Murkowski of Alaska.