But if he gets in, Mr. Christie will have to explain his repeated insistence that he is not ready to serve in the White House. “You have to believe, as I’ve said before, in your heart and in your mind that you’re ready,” he told The Times in February. “And I don’t believe that I am.”

He will also immediately face the challenge of raising money. The excitement among some very wealthy donors suggests that might not be too difficult. But running for president requires a large fund-raising organization and Mr. Christie would start millions of dollars behind his rivals.

Right away, Mr. Christie and his campaign advisers would face the challenge of his schedule. Every day that he spends on the phone with donors is a day he’s not spending in Iowa, New Hampshire or South Carolina — places that his potential rivals have been visiting regularly for weeks.

And then there is the question of his temperament.