The final couple of weeks before Iowa and New Hampshire are often among the most volatile of the primary season. The candidates start attacking one another, voters start making up their minds, and even the smallest shifts can bring a wave of media coverage that reshapes the race at a crucial stage.

There is no way to know whether a new poll from the American Research Group is correct in suggesting that such a story is unfolding in New Hampshire. It shows John Kasich surging into a strong second place in the Republican race with 20 percent of the vote.

If true, it would be a big turn in the race.

I can’t say whether Mr. Kasich has really surged in New Hampshire; it is always better to look at all the evidence, and there just aren’t many recent polls in New Hampshire.