Great, another sleazbag.
But here's the thing: Our country cares more about these type of B.S. stories instead of the issues. It's time to move on, America.
To be honest, Adultery is a pretty despicable action, especially for those claiming to be some sort of Christian (I don't care how liberal you are, the 10 commandments are the 10 commandments, and it literally says "thou shalt not commit adultery".) (Bentley is Baptist). Even if you're not religious, the fact still remains that the wording of most marriage vows calls for devotion "until death". Committing adultery is hardly maintaining that devotion (provided you don't have prior permission from your spouse).
Obviously making adultery illegal is unrealistic (What are we supposed to do to enforce it, ultra-theocrats? Abolish the 4th amendment so that Police can arbitrarily search through homes for adulterers?), but that doesn't mean we should be voting adulterers into office.
Clearly, it is wrong, but it doesn't automatically mean someone isn't fit to be a political leader. However, if it's like Berlusconi-levels of adultery or a situation like John Ensign's, where he broke the law as a result of his stupidity, then they should resign, yes.