Frank Underwood.
To what extent is his method of "ruthless pragmatism" effective? In his character, what would you say are his weaknesses?
I find his greatest weakness in changing others, When someone opposes him and he can't persuade them otherwise, he... becomes let's say very hands-on (if you haven't watched S1 finale or first episode of S2). You'll notice for a man who usually hides nothing, or gives orders to other people, he doesn't even tell those close to him what he committed.