Following the Republican National Convention in Tampa, Florida, 40 percent of voters said they were more likely to support Romney for president after the convention, compared with 38 percent who were less likely.

The net impact of each convention was calculated by subtracting the percentage who said the convention made them less likely to vote for the party's nominee from the percentage saying it made them more likely to vote for the nominee. The net impact of +2 this year is below the +5 and +3 for the GOP conventions in 2008 and 2004, respectively.

Romney's acceptance speech last Thursday night also scored low. Thirty-eight percent of respondents said the speech was "excellent" or "good," which was lower than the 47 percent who said John McCain's 2008 acceptance speech was "excellent" or "good."

However, Gallup noted immediate reactions to the convention did not by themselves predict who would win the election.

The Tampa convention officially endorsed Romney as the Republican Party's candidate for president. President Barack Obama is to be named the Democratic Party's nominee this week.