They go by many names... Progressives, Liberals, Democrats, Socialists...
And here's why they win. They've convinced Americans that the battle lines are "left vs. right", "republican vs. democrat", "liberal vs. socialist".
This keeps people fighting amongst themselves, arguing whether their shade of grey is the "right" way to run a government.
It's pretty obvious to an outsider what the power division is in America. It's pretty obvious if you look at america's decline over the past decades & see how authority has been consolidated & maintained. It's pretty obvious if you look at how fear and uncertainty are utilized by the government to herd the population in the direction they want them to go.
The battle lines are: "rich vs. poor". They almost always have been.
Until people understand that, and as long as people believe that stupid side issues like minor health care reforms (and yes, they are quite minor), gay marriage, abortion, gun ownership, immigration reform, etc are what is going to ruin / save the country, the longer the people in power stay that way.