Romney fell below 43 percent for the first time, claiming 41 percent of likely primary voters in the Granite State. Ron Paul was second at 18 percent. Santorum came in at 8 percent, followed by Newt Gingrich at 7 percent, Jon Huntsman at 7 percent, and Rick Perry and Buddy Roemer at 1 percent each.

Santorum, whose surprise, late surge in the Iowa caucuses nearly toppled Romney in the Hawkeye State, has gained support every day in New Hampshire since Suffolk began its daily tracking.

Paul climbed 4 points, up from 14 percent on Wednesday.

“This is the first full day that voters had the opportunity to digest the final results of the Iowa caucuses,” said David Paleologos, director of the Suffolk University Political Research Center in Boston. “The result is that the same three winners in Iowa are the top three contenders in New Hampshire.”

Since his Iowa victory, Romney has become the focus of attacks from his rivals, who are calling into question his conservative bona fides. Gingrich ran a full-page ad in the influential conservative newspaper The New Hampshire Union Leader on Wednesday branding Romney as a “timid Massachusetts moderate.”

While his lead in New Hampshire seems safe, there are signs that attacks against Romney may be working. The former Massachusetts governor’s slight decline came from a dip in support from three of New Hampshire’s most conservative counties.