Fewer than half of U.S. adults identified as Democrats in 2009, the first time the number has dipped below that threshold since 2005.

Forty-nine percent of adults said they were Democrats or leaned Democratic while 40.7 percent of adults polled said they were Republican or leaned Republican. By comparison, 51.5 percent of adults identified as Democratic in 2008 while 39.8 percent said they were Republican.

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The numbers are an aggregation of Gallup polls on the question from last year and were released Wednesday.

Gallup's analysts noted that the numbers are partially the result of a sharp decline in Democratic support over the course of 2009, President Barack Obama's first year in office. 

During his first year, the president pushed a number of major pieces of legislation such as the federal stimulus package, cap-and-trade climate legislation and the healthcare overhaul.

At the same time, the U.S. economy continued to suffer from a precipitous decline that began in 2008, the last year of President George W. Bush's second term.

In March 2009, 51.7 percent of Americans identified as Democrats, and by December, the figure dropped to 47.2 percent. Republican support climbed from 38.7 percent to 42.2 percent over that time frame. 

However, Gallup cautioned that the rise in GOP support was mainly bolstered by "soft support" among Republican-leaning independents.

"The percentage of Americans with a stronger attachment to the GOP — those who initially identify themselves as Republicans — was stable and, if anything, showed a slight decline over the course of the year," Gallup said.

Meanwhile, independents increased from 34.9 to 36.6 percent between 2008 and 2009.