For the politicians, it's about Power 100%. Don't make the mistake of thinking that they are stupid or that they really believe the feelgood Liberal nonsense that they spout. These guys are smart, and they know exactly what they want and how to get it. They are elitists, they really believe that they are an elite few and everyone else is just mindless ciphers who are stupid, don't matter, and need to be told what to do by the elite. They want ever-increasing amounts of power and authority for themselves. The feelgood liberal hippy BS is just what they use to get the ignorant masses to give them more power. Gun control is just another way of increasing their power over you. Preventing armed revolution at some point is probably in the back of their heads too.
Rather then the Dem's demands for gun control being political expidiency, I believe that the resistance of many prominent Republicans to gun control is political expediency. They are power-hungy elitists just the same, they have just detemined that taking certain positions will keep them in office to pass other laws that will gradually reduce our freedoms and increase their power.
There are some idealists in there who really believe the party line, moreso on the Republican side I think, but they rarely last long enough and rise high enough to really matter.