When Gallup began asking about ideological identification in all its polls in 1992, an average 17% of Americans said they were liberal. That dipped to 16% in 1995 and 1996, but has gradually increased, exceeding 20% each year since 2005.

The rise in liberal identification has been accompanied by a decline in moderate identification. At 34% in 2013, it is the lowest Gallup has measured, and down nine points since 1992. Moderates had been the largest ideological group throughout the 1990s, and competed with conservatives for the top spot during the 2000s. Since 2009, conservatives have consistently been the largest U.S. ideological group.

The percentage of conservatives has always far exceeded the percentage of liberals, by as much as 22 points in 1996. With more Americans identifying as liberals in recent years, and conservative identification holding steady, the conservative advantage of 15 points ties the 2007 and 2008 gaps as the smallest.