The falling concern over the economy seems largely driven by Democrats. While 63 percent of Republicans and 62 percent of Independents identified some sort of economic concern, only 53 percent of Democrats did. That's a sharp break from earlier in the year, where economic concerns across party lines were on par with one another. The 53 percent of Democrats naming economic issues is down from 72 percent who did so just two months ago.

Interestingly, the tragedy in Newtown, Conn., does not seem to have dramatically changed Americans' attitudes about the nation's top concern. Only 4 percent of those surveyed said guns or gun control were the top priority, and only 2 percent said crime or violence should be the country's chief concern.

Still, even those numbers represent more significant movement than with other tragedies. After the shooting in the Aurora, Colo., movie theater, only 1 percent saw "crime" or "violence" as the most important problem, a similar response to the one garnered in the aftermath of the shootings in Tucson, Ariz., that injured former Rep. Gabrielle Giffords (D-Ariz.).

"While no doubt every American was deeply saddened by the events in Newtown, Conn., most do not view crime or gun violence as the nation's preeminent concern, at least right now," said Gallup's Andrew Dugan. "However, this most recent shooting has had slightly more of an impact in terms of changing some Americans' national priorities than recent mass killings."