The easy word is ability. Very hard to define, and yes, it deserves a thread of it's own. Excellent subject. I think it requires a further distinction as to a "good" public official vs a "bad" one. To another extent, the level of public service. An "able" public official (this day and age) to me is the one who brings the combination of skills to the table that best allows him/her to effect a particular set of agendas, while at the same time understanding a hell of a lot of balances and trade offs. There is no black and white in American politics. If one doesn't understand grey, stay home.
One problem to me, is the real dogfights are at the lower level. You end up getting people into "junior" office that start running up the chain to State or National legislature because of who they know and what they will support. Then, when the political prize gets bigger, they are trapped in the middle for a while. The survivors are those who are generally there because they want to be something, not DO anything.
I won't paint with a total brush, because I know there are good people out there. But for the most part, welcome to DC. I don't care what your affiliation is. That's the way it is.