On December 4, Gallup Polls released a new poll asking U.S. voters about their partisan affiliation. Gallup periodically does this poll. When respondents answer that they are “independent”, they are asked if they lean toward either the Republican Party or the Democratic Party, and leaners are then classified with that party.
The latest figures: Democratic 44%; Republican 37%; other 19%. See here. Thanks to Political Wire for the link.