"Liberal" is no longer a dirty word - or at least, it's not as dirty as it used to be. On Election Day, 25% of voters claimed to be liberals - a jump up from 22% from 2008, and from 17% at Reagan's re-election in 1984.
Why are more people now happy to be liberal? A few factors could be at work. Demographics that mostly self-identify as liberal are growing apace - including Latinos, religious non-believers, and college graduates. And the perception among Democrats that Obama is both cool and a liberal has probably made the label more fashionable - or at least less shameful - than it once was.
Note that "liberal" is still far less popular than "conservative" as a form of self-branding. 35% of voters called themselves conservatives on Nov 6, and that number has stayed roughly the same for decades.