Earlier quoted context omitted.
Well, everybody calls them liberals; they even call themselves liberals (when they're not calling themselves progressives, which is an even stronger code word for "left-wing"). If your argument is that they aren't "true" liberals, then who are the "true" liberals?
George McGovern. Walter Mondale. Lyndon Johnson. Franklin Roosevelt. William O. Douglas. Thurgood Marshall. There are liberals in the government today, but they are a minority and wield very little power. Here's an interesting historical perspective of the Supreme Court: http://en.wikipedia.org/wiki/Ideological_leanings_of_U.S._Su... And a contemporary analysis of Congress: http://thatsmycongress.com/house/ http://th…
As for your list of "true" liberals, McGovern is the only one who strikes me as consistently furthering "liberal" positions (by which I mean "liberal" by the definition you appear to be using--see below). Mondale didn't strike me as consistently furthering much of anything. Johnson got us deep into Vietnam. FDR got us into World War II (by which I don't just mean he was President when it started, I mean he consistently took actions, often covert ones, that were calculated to get us into the war). Douglas voted with the majority in Korematsu v. United States (his positions did change over time, so, for example, he wrote the majority opinion in Griswold v. Connecticut; but that just points up the fact that he wasn't always consistent). Marshall did win Brown v. Board of Education, but while education in the US is more integrated today than it was then, I question whether it is any more equal, unless it's in the sense that it's more equally bad. (To be fair, Marshall was pretty consistently liberal in his opinions as a Supreme Court Justice.)
Of course, from your point of view, this just makes the case stronger that "true" liberals have very little power in the US. But from my point of view, it makes the case stronger that your definition of the word "liberal" is not a useful or historically accurate one.