For the fourth straight month, the number of people identifying themselves as Republicans has decreased. For the third straight month, the number of people identifying themselves as Democrats has also decreased (see history).

A Rasmussen Reports national telephone survey of 15,000 adults in May found that just 30.8% now say they’re Republicans. That’s down slightly from last month and down more than six percentage points from the GOP peak of 37.3% during Election 2004. The number of Republicans has been falling fairly steadily since the middle of 2005.

However, the survey also found that the number of people identifying themselves as Democrats has fallen to its lowest level in seventeen months (since January 2006). Democrats gained about two percentage points of support during 2006 and peaked at 38.0% in December of last year. Since actually taking control of Congress, Democrats have given back most of those gains. Today, 36.3% say they belong to Nancy Pelosi’s party.

As a result, the number not affiliated with either major party has jumped to another all-time high—32.9%. That’s up nearly nine percentage points since Election 2004 and means that there are now more politically unaffiliated adults than Republicans (see related stories on the possibility of an independent White House bid by Michael Bloomberg and the how a successful independent campaign could deadlock both the Electoral College and House of Representatives).

These results are based upon tracking surveys of 15,000 adults per month. The margin of sampling error is less than one percentage point, with a 95% level of confidence. Please keep in mind that figures reported in this article are for all adults, not Likely Voters. Republicans typically do a bit better among Likely Voters (in fact, the two parties ended up even among those who showed up to vote in 2004).

The Democrats' net advantage over Republicans is now 5.5 percentage points, unchanged from a month ago. That’s down slightly from the peak advantage of 6.9 points following Election 2006. However, the Democratic edge remains larger than at any point prior to the fall of 2006.

A recent tracking survey found that voters trust Democrats more than Republicans on ten key issues including taxes and national security. Democrats continue to enjoy a large advantage on the Generic Congressional Ballot.

During the month of May, President Bush’s Job Approval fell to the lowest level ever recorded by Rasmussen Reports—33%. The President’s Job Approval ratings have tumbled every time immigration reform dominates the news.

Please review Monthly data from January 2004 to April 2007.

Rasmussen Reports continuously updates favorability ratings and general election match-ups for all Democratic and Republican candidates. Also available are continuously updated ratings for Members of Congress, Other Political Figures, and Journalists

Rasmussen Reports releases updated polling data for the Democrats’ nominating contest are updated on Mondays. Republican results are updated every each Tuesday.