I’m not a Cain fan. I thought he was completely unqualified before this. And I am voting for Newt. According to the Catholic faith, if Newt made a good confession when he converted, his prior adultery was forgiven. If Newt is reconciled with God, who am I to hold his past against him?
Being forgiven by God does not imply a grant of trust from your fellow mortals, who do not have the advantage of divine insight as to future behavior. From our lowly view, we are fully justified in not trusting a person who has repeatedly broken a solemn vow. I am not saying such a defect can never be overcome in this life. But there is no argument from moral superiority that we should ignore untrustworthy behavior in hiring someone for the highest position of trust in our system.
As for the role of God's law in electoral politics generally, I think there are other commandments besides the prohibition on adultery in play here. Listed among the Ten is the commandment not to bear false witness against one's neighbor. This is God telling us he puts defamation on the same level as adultery, murder, theft, etc. It is a very serious crime in God's eyes, and that is a big reason why I have been very careful not to aid and abet the slander machine. My own soul stands to lose if I carelessly handle another person’s reputation.
And I'm not sure what Catholicism teaches on the matter, but in the Reformed faith, it is not enough to just avoid the sin yourself. You are culpable to the degree you allow it to go unchallenged in others. If you sanction it, whether actively or passively, you are part of it. For everyone who is sincere about being faithful to God's law, it is a moral duty to challenge defamation in their circle of influence. If something bad is proven true, so be it. If there is no proof, it is a blight to one's own soul to either repeat it or to let others repeat it unchallenged.