DENVER, Colo. -- Mitt Romney surprised the crowd at the Conservative Political Action Conference on Thursday by stopping by unannounced, revving up the crowd to recruit more voters and help him win Colorado.
"It's fun to be here and feel all the energy that you have here. I know all of your enthusiasm, I know of your passion for America ... but for that to happen you guys are going to have to cheer here and then go out and knock on doors and get people who voted for President Obama to see the light and come join our team," he said.
Four of Romney's sons were scheduled to speak at the event. When they came out, Romney's eldest son, Tagg, said his brother Ben was unable to attend because of his medical residency.
"We found a fill-in for him and we want to bring him out," Tagg Romney said, followed by his father walking on stage.
Although the surprise guest's identity had already started to leak out on Twitter, the few hundred conservative activists in the dark ballroom hadn't yet received word. When Romney walked out on stage, the crowd erupted with shocked and delighted applause.
"I heard my boys were going to be here -- I couldn't resist," Romney said.
Romney gave his standard stump speech, beginning and ending with a reference to the presidential debate on Wednesday, which most media outlets say he won.
"I thought it was a great opportunity for the American people to see two very different visions for the country," Romney said. "I think it was helpful to get to describe those visions. I saw the president's vision as trickle-down government, and I don't think that's what America believes in."
Amanda Terkel contributed reporting.