According to Pew data, 46 percent of Democrats and Democratic-leaning voters now identify as liberal—up from 28 percent 10 years ago. Meanwhile, the percentage who say they’re moderates has dropped from 44 to 37. The number of conservatives continues to drop, too. But these changes most likely reflect the exodus of right-leaning Democrats as both parties become more ideologically homogeneous. It doesn’t necessarily mean that there’s been huge growth on the party’s left wing.

Then there’s the question of what it means to be “liberal.” Among progressive pundits, there’s a debate between “liberals” (for example, Obama Democrats) and “leftists” (progressives with more socialist inclinations). But Pew, which maintains the best longitudinal data, doesn’t subdivide that way, and it’s hard to know what voters mean when they self-identify as liberal. For example, support for LGBT rights was once a litmus test for American liberalism, notes Amy Walter, national editor of the Cook Political Report. Now that view is the consensus within the Democratic Party—and gay marriage is largely accepted among Republicans, too. So what is liberalism now?

“Is it the Bernie Sanders view on economic issues? Is it views on social issues?” Walters asks. “Can you have progressive views on social issues, but if you don’t agree with Bernie Sanders’s opinion on government size, are you not a liberal?”