On average, 47 percent of Americans in 2012 said they were Democrats or Democratic-leaning independents, compared to 42 percent who were Republicans or Republican-leaning independents, Gallup reports.
The Democrats' 5-point margin is an uptick from 2010 and 2011, when the two parties ran almost even.
Nearly all of the change comes from independents leaning in a different direction, rather than any shift in beliefs among party stalwarts. Independents in 2012 were more likely to lean toward Democrats than Republicans by 2 points -- a reversal from the previous year, when they favored the GOP by 4 points.
The numbers of Americans identifying as belonging to either the Republican or the Democratic Party remained basically the same, while the total number of independents matches 2011's record high.
Levels of party identification regularly shift, especially among less dogmatic voters.
As Gallup notes, Democrats have historically held a lead in party ID:
Gallup has measured party identification and leaning consistently since 1991. During that time, Democrats usually have held an advantage, including the high margin of 12 points in 2008, the year President Barack Obama was elected. Republicans have held an advantage in only one year -- 1991, when President George H.W. Bush enjoyed record-high approval ratings after the Persian Gulf War. The two parties were essentially tied in 1994-1995, 2001-2003, and 2010-2011.
Gallup's party ID numbers for the last year come from telephone interviews of 20,800 adults, with a 1 percent margin of error.