"You'll notice last night that I didn't say his name once. I did that for a specific reason: Because I believe he is irrelevant," Christie said in a recording of the event. "And he's irrelevant because he made himself irrelevant.
"I've never met a more inconsequential president in terms of moving and shaping debate in our country, shaping the legislative process," he added. "He allows Congress to run the show. I've never seen a president like that who has so abdicated his responsibility to be a national leader."
Before he was elected governor, Christie said, Democrats had controlled the state for a decade and New Jersey saw zero job growth, 115 increases in taxes and fees and was losing businesses to neighboring states.
Christie said he enjoyed his role making the case against Obama, and "I know he was watching, because he's the thinnest-skinned politician in America."
During the remaining days of the convention, Republicans need to show why Romney would do a better job. And while Christie said the former Massachusetts governor has the résumé and experience to be president, he also has the heart.
Christie drew laughs during a story about how Romney called him in October, after Christie had insisted again that he wasn't going to run for president, and asked if they could have lunch.
"What are you gonna say? Sure, all right," he said, but with four kids, the house had to be cleaned and they had to coach the children to greet the Romneys politely and "then make themselves scarce."
Things were going well until his 11-year-old came streaking toward Romney on a pair of Rollerblades and stopped a foot from their guest. Christie said Romney was unfazed and asked him a series of questions about skating and hockey before the 4-year-old daughter, jealous of the attention, started doing cartwheels near the table.
Romney, concerned about her hitting the table, took her by the hand to the lawn.
"And I see her out there with him," Christie recalled, "and she's showing him how she does cartwheels and he's helping her and she's showing him how she does handstands and he's holding her feet, and I'm watching this back and forth, saying to myself, 'Look at this guy.' "
"It tells you something about his heart," Christie said. "This guy's got the heart that I can trust to sit behind that desk and understand the actions he takes sending young men and women into war, making decisions of extraordinary consequence for their future. He won't just think about it with his head, but he'll feel it with his heart. That's the kind of president I want again."
Christie concluded by encouraging Utahns who are in a safe Romney state like those in New Jersey are in a safe Obama state to reach out to friends in battleground states and make sure they are supporting Romney, too.
The brunch, was arranged by Utah Gov. Gary Herbert well in advance of Christie being selected as the keynote speaker. Herbert will also host Christie at his annual fundraising gala next month.
Robert GehrkeTwitter: @RobertGehrke