The poll found 46 percent of registered voters favored Romney in Aug. 31-Sept. 3 Gallup Daily tracking, down a statistically insignificant 1 point from the 47 percent who preferred Romney Aug. 24-27, the four days leading up to the Republican convention in Tampa, Fla.
The Gallup finding was released the same day a CNN/ORC International poll showed a 1-point convention bounce, which CNN said was a normal result in the modern political era.
The CNN poll showed Romney tied with President Barack Obama at 48 percent support among likely voters. Before the Republican convention, Obama led Romney in the CNN/ORC poll 49-47.
"The Republican convention had at best a mild effect on the presidential race, and from a statistical viewpoint, no effect at all," CNN Polling Director Keating Holland said.
Keating said the poll suggests Romney's campaign may have gained some support among some voters but "at the expense of turning off another group of voters."
Romney gained 7 points among affluent Americans but lost 4 points among lower-income voters, CNN said.
The Hill Tuesday said a Pulse Opinion Research poll conducted Sept. 2 found 52 percent of U.S. voters believe the country is worse off now than it was four years ago and 54 percent say Obama does not deserve to be re-elected.
The poll of 1,000 likely voters has a 3 percentage point margin of error.
The ORC International poll of 1,005 adults was conducted Aug. 31-Sept. 3, with an overall sampling error of 3 percentage points and a sampling error of 3.5 percentage points for registered and likely voter questions.
The Gallup Daily tracking poll of Aug. 31-Sept. 3 surveyed 1,827 registered voters and has a maximum margin of sampling error of 3 percentage points.