The summer swoon is likely due to a confluence of factors, some outside the president's control. His approval numbers in the winter months are aided by momentum following his two successful election campaigns, while he sees a spike in the spring thanks to the capture of Osama bin Laden in May 2011. Gallup also suggests that Americans may be less closely monitoring the news in the summer months, making them more reluctant to say they approve of the president's handling of his job.

But Obama is also likely being penalized for his annual vacations to Martha's Vineyard, as well as summertime gas prices and little legislation passing during the August congressional recess.

A survey released by YouGov last week found a plurality of Americans — 44 percent — believe that the president takes too much vacation time, with just a third of respondents disagreeing.

Still, Gallup's Jeffrey M. Jones says, the trend could be an encouraging sign for the White House, which will need to rebuild political capital before tough fights on the federal budget and debt ceiling this fall.

"The decline in his approval rating from 49 percent in May of this year to 45 percent in August to date may reflect this seasonal pattern in how Americans view the president as much as anything he is or is not doing at the moment," he said in a statement.

The annual summer decline is not unique to the Obama White House. Both President Clinton and President George W. Bush also saw their average approval rating lag during the summer months, although neither as severely as for Obama.