The number of Americans who consider themselves to be Democrats inched up again in December to 41.6%. That’s up two-tenths of a point since November and the third straight monthly increase in the number of Democrats.

Only once since Rasmussen Reports began tracking this data on a monthly basis in 2002 has the number of Democrats been higher. In May, as the Obama-Clinton primary battle neared its conclusion, 41.7% of Americans said they were Democrats.

At the same time, the number of Republicans declined a full percentage point from 33.8% in November to 32.8% in December. That’s the lowest number of Republicans since August. The number claiming allegiance to the GOP peaked in September at 34.4% as the party enjoyed a convention bounce and Sarah Palin was picked as the party’s Vice Presidential nominee.

The number not affiliated with either major party inched up from 24.7% in November to 25.6% in December.

Rasmussen Reports tracks this information based upon telephone interviews with approximately 15,000 adults per month and has been doing so since November 2002.

Currently, the Democrats enjoy an 8.8 percentage point advantage over Republicans. Two years ago, in the December after Democrats regained control of Congress, they enjoyed a 6.9 percentage point advantage over the GOP in terms of partisan identification. That was their biggest advantage ever prior to 2008.

However, once the Democrats actually gained control of Congress, their partisan advantage began a slow, steady decline that lasted a full year until the Presidential Primary season began (see history from January 2004 to present).

These results are based upon tracking surveys of 15,000 adults per month. The margin of sampling error for the sample 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 are a bit more likely to participate in elections than Democrats.

The Rasmussen Reports daily Presidential Approval Index shows that Barack Obama has earned favorable reviews during his first two months as President-elect. Democrats continue to have a significant advantage on 10 key issues tracked by Rasmussen Reports and lead on the Generic Congressional Ballot.