He saved his criticism of Obama for the end of his speech. The president, he said, should spend less time reading polls and more time trying to shape public opinion. "Real leaders don’t follow polls," he said. "Real leaders change polls."

Romney and the Republicans, Christie said, would do that in Washington. "It’s time to end this era of absentee leadership in the Oval Office and send real leaders to the White House," he said.

In so many ways, the New Jersey governor is the antithesis of the Republican nominee. Christie the politician is the direct opposite of Romney — a bluff, brash New Jersey prosecutor who likes nothing better than to verbally attack his attackers. Romney is modest and reserved, and has attacked rivals in debates but more often shows his sometimes awkward politeness to the people he meets on the campaign trail.

Christie has reveled in his reputation as a blunt-talking governor, rarely passing up an opportunity to tell an audience about his most recent confrontations — whether with Democrats in the New Jersey legislature or constituents who challenged him. Romney has found it difficult to talk about himself or bring undue attention to his actions. It is a measure of how opposites attract that Romney wanted Christie to make a case for him in Tampa.

Still, the governor is no mere sidekick. He still can’t go far without someone asking about his presidential ambitions. On NBC’s "Today" show Tuesday, Matt Lauer asked, "A lot of people look and say this may be the moment that he launches his bid for the next nomination. Is there truth to that?"

The answer was not definitive. "I doubt it," Christie replied, " ’cause I think Mitt Romney will be at the convention in 2016 being renominated for a second term. And so then you’re talking about 2020 — long, long way away."

Before that, he had to deny a report in the New York Post that said he had turned down the vice presidential nomination because he didn’t think Romney would win.

At some point, Christie may be able to stop batting away speculation about his aspirations and began to act on them. That could be soon or not so soon, depending on what happens in November. He may be his own man, but for this time and place, he played the role he was assigned.