Walker gets 18 percent compared to 16 percent for Bush.
A new Quinnipiac poll suggests Hillary Clinton could be beatable in Virginia and Colorado.
The percentage of likely caucus-goers who viewed Romney unfavorably rose by 10 points.
The economy had been voters' chief worry for the last six years, Gallup says.
A strong majority said they were contacted by campaigns too many times and saw too many ads.
The campaign post-mortem is "an admonishment to Democrats," a pollster says.
Recent polls found growing support for ties among Cuban-Americans and nationally.
No Republican presidential contender is within 5 percentage points of Clinton.
Rep. Cassidy (R) leads Sen. Landrieu (D) 56-41 percent in Rasmussen poll.
Thirty-six percent have a favorable view, dropping the party below the GOP.