LIVINGSTON, N.J. — Gov. Chris Christie declared an uphill candidacy for president on Tuesday with New Jersey-style swagger, unconcealed disgust for Washington and a high regard for his own candor, vowing that “there is one thing you will know for sure: I say what I mean and I mean what I say.”

Relying on his biggest, and perhaps his last, remaining advantage in a field of better-financed and better-liked rivals — his personality — Mr. Christie portrayed himself as the only candidate in the Republican field who is forthright and forceful enough to run the country.

“We need strength and decision-making and authority back in the Oval Office,” he said.

Pacing the stage without a prepared text and raising his voice to a shout at times, he vowed to campaign and govern as a colorful teller of difficult truths, even if “it makes you cringe every once in a while.”

“I am not running for president of the United States as surrogate for being elected prom king of America,” Mr. Christie said inside the gymnasium at the high school where he was president of his class all three years.