Newt Gingrich obviously doesn’t really want monogamy. He’s probably polyamorous. After all he married all of his mistresses. There’s nothing wrong with polyamory. It’s a perfectly valid arrangement among consenting adults.
Unfortunately, he behaved rather badly towards his wives. In his defese, it probably took him a long time to admit to himself what he really wanted, maybe he still hasn’t. He suppressed his socially unacceptable feelings and tried to pass for “normal”, and then found himself married when he finally realized that he doesn’t really want monogamy. But at that point he should have been honest with his first wife instead of cheating. He needed to “come out” as non-monogamous, not try to hide it and cheat. Then he should have either stayed in the marriage and been monogamous, or gotten a divorce before starting another relationship. He certainly shouldn’t have gotten married again to another woman who wanted monogamy.
All of that is a personal failure and a tragedy for his wives, but I don’t think it should be “on the table” for political attacks.
However, in his political career he tried to play the social conservative for political gain. His attacks on Bill Clinton are particularly glaring in this respect. Now perhaps, deep down, he’s not really a hypocrite, but rather a political opportunist. He may not really feel that what Bill did was wrong. Maybe he just pretended to be outraged to score political points. This aspect I think deserves public criticism and is a perfectly acceptable target in the political arena. The fact is that his political actions were either hypocritical or based on expediency and opportunism, not principle.
Unfortunately, in our current system of voting for the lesser of two evils even that would probably not prevent me from voting for him if all the other options were worse.