It is not hard to imagine why there was a larger shift in Alaska than elsewhere. Mr. Sullivan won the Republican nomination after the release of the first wave of data, an event that can often cause a candidate to get a bump in the polls. A possible third-party challenger, Joe Miller, also announced that he wouldn’t enter the race, perhaps leading some number of his supporters to switch from “other” to the newly minted Republican nominee.

And Mr. Begich has recently been criticized for an advertisement accusing Mr. Sullivan of authorizing the early release of a sex offender who is now charged with murdering an older couple and sexually assaulting their 2-year-old granddaughter. A clerical error in a plea agreement in 2009, which led to the early release, happened before Mr. Sullivan became attorney general. Mr. Begich withdrew the advertisement, and Mr. Sullivan withdrew the ad he ran in response, after complaints from the victims’ family and concerns from the family’s lawyer about interfering with the trial.

The other swing came in New Hampshire, where Scott Brown, the Republican challenger, narrowed the lead of Senator Jeanne Shaheen from 10 to 6 percentage points. None of the swing came from respondents switching from Ms. Shaheen to Mr. Brown, though a net 3 percent of respondents switched from “other” or “undecided” to Mr. Brown. Additional gains will be more challenging, since there is now a smaller gap between the number of “other” and “undecided” Republican and Democratic partisans.

The new results also reflect an adjustment, or screen, to capture likely voters. The result is an electorate that is older and whiter, and more Republican, than the overall pool of registered voters. The white share of likely voters is two percentage points higher than the white share of registered voters; the share of likely voters over age 65 is 4 percentage points higher than among registered voters.