I was in an online conversation elsewhere regarding the difference between a “liberal” and a “progressive.” I maintained that there is none, that it is two different labels for the same person. The reason is that conservatives turned “liberal” into a pejorative and, as is typical of the genre, liberals freaked out and began calling themselves “progressives” instead. Liberals pretty much always run from a fight, either changing the subject, or just surrendering to the opponent and calling it a “good compromise.”
Conservatives, on the other hand, love a good fight. Liberals tried to turn the label “conservative” into a pejorative and it didn’t work. Conservatives reacted with a sort of collective, “Hell yes I’m one of those. Suck on it.”
Full disclosure, here. I took a test one time; answer a whole bunch of questions to determine if you are a liberal or a conservative. Not only did I score as a liberal, I would up grading to the left of Desmond Tutu. That doesn't mean that I cannot recognize that liberals are really bad at politics.
The two movements approach policy in a similar manner. Conservatives have strong principles and will adhere to them at all costs, even losing elections if needed to stand up for their principles. If they elect a Republican, for instance, and he raises taxes, they will throw his ass out of office to prove their point, even if it means electing a Democrat to do so. Witness George the Elder.
That’s part of the current “disarray” that the Republican Party finds itself in today. None of the current candidates is sufficiently adherent to the principles that are the backbone of the party, and so party loyalists are thrashing around a bit looking for someone who meets their criteria. Pundits decry the wingnut candidates as being unable to win in a general election, but that doesn’t matter to conservatives. Adhering to their principles is more important than winning.
Liberals, not so much. They have some ideas, but not much in the way of actual principles. They aren't all that coherent on what those ideas are, really, and they don't require adherence to them in any case. They elect a guy to restore civil liberties and constitutionality and if he doesn't do it, well, they weren't all that certain about the civil liberties and constitutionality thing anyway. Maybe things were only bad because it was a Republican doing it, so they'll reelect this guy regardless, because he's a Democrat whatever he does.
Witness Barack Obama, who has done almost nothing which liberals hold dear, but who is utterly unchallenged for the Democratic spot in 2012 and, in fact, who no elected Democrat even dares criticize to even the slightest degree.