Person "A" is a smart guy. Grew up in the 70s and/or 80s. Did above average in school. Got married to a great wife. Two nice kids. Very intelligent, thoughtful, intellectually curious. Has done a little for his community.
However... In the 90s, he got into an argument with a friend at work over email. He said a few nasty things that he immediately regretted. He also sent some email forwards of some jokes, some of which may have been based in racial or ethnic stereotypes. His oldest kid has been in a few fights at school. His wife's politics clash with his own.
Person "B" is of average intelligence. He's not dumb, but he's not the smartest guy in any room he walks into. Decent school career, wife and kids. Pretty vanilla personality. Set in his beliefs, however, he's never really interested in new information. Anyone who disagrees with him just "doesn't get it," and he'd rather not spend his time dealing with them. Nothing in his past that can paint his as "evil," (not like that racist, poor parenting, elitist, waffling person "a.").
Person A, though probably more qualified, and better for the job, is smart enough never to run. He knows he, his family, his past, everything will be run through a grinder as politics is far more about personality and "sides" than actual ideas. His life and those around him is infinitely better by just staying at home and not entering that arena.
Person "B" isn't so worried. After all, he's never really gotten involved in that email stuff. He's never really done anything of note, but he's also not on record of doing anything people could disagree with. He's not very smart, and doesn't have a lot of new ideas, but that's ok, because he made up his mind about politics years ago, new information and changing world be damned.
"Let's all get the same girl pregnant, tonight!"