After claiming for days that nothing went wrong, Sen. Marco Rubio (R-Florida) directly said Tuesday that he made a mistake in last weekend's primary debate.
"On Saturday night at the debate, I dropped the ball," Rubio wrote to his supporters. "I want you to know that will never happen again."
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Rubio performed strongly in last week's Iowa caucuses, defying polls to come in third and just behind national front-runner Donald Trump.
But then the knives came out for the presidential candidate, and many of his rivals started pounding him.
Notably, New Jersey Gov. Chris Christie (R) confronted Rubio at the Saturday debate. Christie ripped Rubio as an inexperienced politician who recited only canned lines. Rubio responded by repeating a line, which many observers interpreted as a gaffe but Rubio said was intentional.
RELATED GALLERY: See photos from Saturday's GOP debate
With 89% of returns in Wednesday morning, Rubio looked as if he would finish in fifth place in New Hampshire after his supporters hoped his third-place finish in Iowa would propel him to second in the Granite State. In his concession speech Tuesday night, Rubio also said he could have done better at the debate.
"I'm disappointed with tonight," Rubio told his supporters. "But I want you to understand something: Our disappointment tonight is not on you. It's on me. It's on me. I did not do well on Saturday night. So listen to this: That will never happen again! That will never happen again."
Rubio also struck a strong optimistic note both in his speech and in his note to supporters. The senator vowed to win both the Republican nomination and the White House.
"We are heading to South Carolina, Nevada and beyond. Make no mistake: We are going to win this nomination," Rubio wrote. "I know how to come from behind," he added.
View his full message to supporters below:
On Saturday night at the debate, I dropped the ball. I want you to know that will never happen again.
We are heading to South Carolina, Nevada and beyond. Make no mistake: We are going to win this nomination.
Throughout my life, I've known tough times. In New Hampshire tonight, I told the story of how when I was young, at one point, my father lost his job as an apartment manager and my family had to move out of our Miami apartment, all in the same week. He had to move clear across the country to Las Vegas to look for work, and the job he finally found, after 20 years as a bartender who'd finally moved his way up a bit, had him starting from scratch again as a busboy.
I know how to come from behind. We're going to show America what leadership and a vision for a New American Century look like.
Friend, if you heard what Bernie Sanders and Hillary Clinton said tonight, you know the stakes: If one of them wins this fall, they will keep up President Obama's efforts to change our country beyond recognition.
I shudder to think what another eight years of President Obama's liberal leadership and lawless actions will look like. Friend, this is our chance to ensure that doesn't happen.
I am the only conservative candidate who can unite our party and beat Hillary Clinton or Bernie Sanders this fall.
If you want a Republican White House next year instead, with the ideas we need to restore America in the 21st Century, then I need your support.
Again, this is just the beginning. I hope I'll have your support as we continue this journey.