I think Paul Krugman has the right take on the fact that South Carolina voters chose a disgraced Republican to represent them in Congress vs. an honest, centrist Democrat:
Look, we have an intensely polarized political system, and in Congress, at least, party affiliation is basically all that matters. When Massachusetts voters chose Scott Brown because he seemed like a nice guy, they were being idiots.
....Maybe, just maybe, you can make a case for choosing the right person for governor, regardless of party. But when you’re sending someone to Congress, all that matters is the R or D after that person’s name. It seems that conservative voters understand that; liberals and moderates should, too.
This wasn't always the case. Today it is. For all practical purposes, we live in a pseudo-parliamentary system of governance, and the only thing that matters in Congress is what party you belong to. If you're a Republican, you're obsessed with Benghazi, Solyndra, Fast & Furious, and debt ceiling hostage taking. If you're a Democrat, you're obsessed with more prosaic topics: passing a budget, keeping social welfare programs from being ripped apart, implementing Obamacare successfully, and asking the rich to help out a wee bit with our long-term budget balancing. Pick your team.