As Ross Douthat has documented, the election of Marc Sanford has belied any claim the Republican Party might make that it stands for traditional values surrounding marriage.
In pretty much every dimension, what Marc Sanford did was worse than what Bill Clinton was impeached for, or what Anthony Weiner was chased from office for. Sanford's behavior had a direct impact on how he did his job, and broke up his marriage. Anyone who supported Clinton's impeachment and voted for Sanford has essentially declared that party ID matter more than anything else. He may have screwed up but he plays for our team; he's a point for our side, or at least he's not a point for the other side.
And, no, this is not merely a malady specific to Republicans or South Carolina voters, as the sudden drop in concern about foreign engagements around 2009 demonstrated.
What this demonstrates is how firm a grip these political parties have on us, and they don't deserve it. They can't offer us a better candidate than Marc Sanford, and expect us to follow along, our own principles be damned. You don't want the other guys to win, do you? This is the most important election ever! Yes, it might be nice to vote for a candidate you can be proud of, but these are desperate times! The other side people want to implement their agenda, which is slightly different from ours! We can't let that happen!
Then, in two or four years, it's the Most Important Election Ever Again.
We've got to stop playing our role in this. We don't have to take every Mark Sanford the parties present to us. We can sit a few dances out if we're not happy with the partners being presented to us.
Regaining our principles will have a much bigger impact on the world than, for example, a special election to finish a House term.