After wavering for weeks, she and her husband, Jeff, who live in Atkinson, have decided to back Mr. Christie.

Whether the support of those who have listened to Mr. Christie will be enough for him to catch up to his better-financed rivals is uncertain. In national polls, he has yet to climb into anything resembling the top tier of Republicans seeking the White House. Conservatives remain suspicious of his tenure as governor. And even without his fingerprints directly upon them, the lane closings on the George Washington Bridge have escalated into a federal prosecution of his confidants.

But two of his biggest electoral threats, former Gov. Jeb Bush of Florida and Gov. John R. Kasich of Ohio, appear to be fizzling. And in New Hampshire, which will hold the first primary in fewer than 80 days, Mr. Christie has accomplished something striking: He has reversed a tide of negative impressions that seemed stubbornly immovable.

After Mr. Christie single-mindedly devoted himself to New Hampshire, 54 percent of likely Republican primary voters now view him favorably, compared with 38 percent who did so in September, according to a Monmouth University poll released in early November.

A few days ago, a poll conducted by Suffolk University and The Boston Globe found much the same: 51 percent of likely Republican voters in New Hampshire have a favorable view of him. He remains far behind Donald J. Trump and Ben Carson, but “likability precedes electability,” said David Paleologos, the director of the Suffolk University Political Research Center.

And tellingly, behind the scenes, rival campaigns that once treated him as an afterthought — or a punch line — are fretting about the possibility of a Christie comeback in the state.