"Mat Helman" asks a lengthy multiple-choice question; I will address each potential answer as they are presented:
Among the GOP Presidential contenders, which personal life blemish would have the biggest negative impact on: A) GOP primary voters, and B) general election voters:
1) Former MA Gov. Mitt Romney strapping his dog to the roof of his car for a drive to Canada.
No impact on either; this is something fun for people who already dislike Romney.
2) VA Gov. Bob McDonnell's master's degree thesis (at age 34) saying that working women were "detrimental" to families and that gov't policy should favor married couples over others.
I think primary voters -- if he runs, and if anyone takes an interest in him -- will consider this raised and settled in his '09 gubernatorial race. If he becomes the nominee, I could see it being one piece in the creation of an overall negative portrait in people's minds.
3) Former U.S. Speaker of the House Newt Gingrich cheating on and leaving his cancer-stricken first wife with his soon-to-be-second wife, and then cheating on his second wife (with his now-third wife).
How much negative impact can something have on someone whose chances are already infinitesimal? BTW, McCain did pretty much the same thing to his first wife, and voters didn't care.
4) MS Gov. Haley Barbour saying that he doesn't remember racism during the civil rights era being "that bad" while crediting the oft-overtly-racist White Citizens' Councils.
I know a lot of people who think this is an asset for Barbour in the primaries, but I think it's probably a push. By the time we get to the general, Barbour will be well-caricatured as a dull-witted Southern hick racist regardless, although this particular comment doesn't help him in fighting that image.
5) TX Gov. Rick Perry hinting at Texas secession at a tea party rally.
Clearly an asset in the primaries -- the base loved it, and the establishment didn't take it seriously. I can't imagine it being a big problem for him in the general, but certainly a small negative there.
6) NJ Gov. Chris Christie awarding a multimillion dollar, no-bid contract to David Kelley, a former U.S. Attorney who had investigated Christie's brother Todd in a 2005 Wall Street fraud case, but "surprisingly" didn't prosecute Todd Christie.
I don't know much about this, and whether there's any there there, as they say, but it doesn't seem like something that would matter unless there are new developments.