Marco Rubio admitted after his fifth-place finish in the New Hampshire Republican primary that he might have let a golden opportunity slip by him.

"I'm disappointed with tonight,...but I want you to understand something....Our disappointment tonight is not on you," he told his supporters. "It's on me. I did not -- I did not do well on Saturday night. So listen to this: that will never happen again."

After a stronger than expected third-place showing in the Iowa caucuses, a string of endorsements from former GOP candidates and polling that showed Rubio gaining support in New Hampshire last week, the first-term Florida senator fell short in the Granite State - finishing behind Trump, Kasich, Cruz and Bush.

Get Breaking News Delivered to Your Inbox

The admission was an about-face for Rubio, who, over the last two days, was unapologetic. He told voters and media outlets that he thought he had had a great debate and felt confident going into Tuesday's primary. A strong showing in New Hampshire, ahead of Kasich, Bush and Cruz would have solidified the argument that Rubio was the establishment alternative to Trump and Cruz.

Instead, it appeared that the debate and the media coverage in the days afterward seemed to have a real impact. CBS News exit polling showed 67 percent of Republican voters rated Saturday's debate as important in their vote, and 47 percent of voters made up their minds in the last few days (23 percent on Tuesday). Of those late-deciding voters, Trump (22 percent) and Kasich (21 percent) received the most support. Rubio attracted just 12 percent.

Rubio had dismissed this idea earlier in the day, while shaking hands outside a polling location in Derry, New Hampshire.

"National media narrative doesn't impact voters especially in place like New Hampshire," he said, indirectly chiding reporters. "These are serious voters, people who have taken their time with the candidates they know the issues better than anybody I have ever interacted with."

But hours later as the results came in, Rubio gave a more sober assessment of where he stood.

"Tonight, we did not wind up where we wanted to be," he said, "but that does not change where we're going to wind up at the end of this process."

Rubio told the crowd in the downtown Manchester hotel ballroom that he had called Donald Trump to congratulate him before coming on stage. "He deserves congratulations. He worked very hard and they did very well," he said, over booing from the crowd.

Wrapping up his brief remarks, Rubio looked past Tuesday's results and forward to the coming contests.

"New England, Maine, Vermont, Massachusetts, we'll see you in a few weeks. We're going to come and win. And South Carolina, we are on the way," Rubio declared as he walked off the stage with his family.