Trump attacks John McCain, without naming him, over healthcare vote #CPAC2018 pic.twitter.com/tg7VJrTYXM— Washington Examiner (@dcexaminer) February 23, 2018

Attendees of the annual Conservative Political Action Conference booed Republican Sen. John McCain on Friday, as President Trump slammed him for voting against a bill last year that would have repealed Obamacare.

"Remember, one person walked into a room, when he was supposed to go this way, and he said he was going this way, and he walked in, and he went this way and everyone said, 'What happened? What was that all about?' " Trump said, eliciting heavy boos from the CPAC crowd.

"Boy, oh boy. Who was that?" he said, alluding to McCain. "I don't want to be controversial, so I won't use his name. OK. What a mess."

McCain joined two of his GOP Senate colleagues – Lisa Murkowski and Susan Collins – in voting against the Obamacare repeal bill that failed in the Senate last September.

Republicans later repealed the healthcare law's individual mandate using tax reform, but the Arizona senator has continued to draw criticism from some conservatives for opposing the earlier chance at a full repeal.

McCain is in Arizona undergoing treatment for an aggressive form of brain cancer.