What're You In For? Adultery?
The fact that Mark Sanford's adultery may be criminal under South Carolina law isn't a black mark on Sanford, but on SOUTH CAROLINA. While as Governor, Sanford probably should have known the relevant statute, I cannot believe that adultery would be punishable by fine or imprisonment. That's kind of appalling, yet unsurprising in a "The Ten Commandments should be the basis of our legal system" kind of way.
Of slightly more importance is the report that some of Sanford's trips to Argentina were taxpayer-funded. That does strike me as serious, although there's no specific causality that's been revealed yet.