In general I am not interested in the private lives of public figures. Read any history and you will discover that many revered figures had disastrous marriages, putrid family lives, massive infidelities, and so on. Thomas Jefferson had a whole second family with his favorite slave. When Admiral Nelson wasn't saving Britain from Napoleon, he was humiliating his wife by appearing in public with his beautiful mistress. Martin Luther King, Jr. took a string of lovers as he traveled the country preaching freedom in black churches, all meticulously documented by the FBI men who were tailing him for J. Edgar Hoover.
So I don't think Newt Gingrich's horrible behavior as a husband in itself disqualifies him as a leader. If I were a Republican primary voter, I would certainly worry that once his infidelity, hypocrisy and casual cruelty become widely known, it might get millions of apolitical people to vote against him, and I would prefer someone without such baggage as my nominee. But then all the other candidates have their own problems.
But his marital grotesqueries are not the only peculiar thing about Newt Gingrich, and this brings me to the theoretical question of what part private lives play in evaluating public figures. I do think that the character or personality of leaders matters. Not in the sense that a man with bad private behavior can't be a great leader; I think he can. But however carefully they prepare themselves for the issues they expect to face, Presidents always end up dealing with the unexpected. Often this happens under crisis conditions, and when it does their character can count for more than their positions on the predictable issues. George W. Bush's incurious, moralistic, bloody-minded, us vs. them attitude toward the world ended up mattering more for America than his campaign promises. I find Obama's intense self-discipline and calm demeanor very reassuring.
So while I am completely uninterested in whether Elliot Spitzer or David Vitter visited prostitutes, I find that the sordid details of Gingrich's second marriage help fill out the picture of who he is. Gingrich is a megalomaniac, and something close to a sociopath in his utter disregard of the rules as they apply to himself. His treatment of his first two wives is of a piece with how he has treated everyone over the course of his career. He was fired by his colleagues in the House for pretty much the same reason his marriages collapsed: because he is completely untrustworthy, lacks any self-discipline whatsoever, and can convince himself that whatever he wants today is absolutely necessary for the salvation of western civilization. One of his main talking points during this campaign has been his scheme to defund or abolish any court that ruled his policies unconstitutional. Nobody else is allowed to make rules that limit what Newt can do, not his wives, not the courts, not the writers of the constitution. I think that matters is deciding whether he should be our president.