I have the reason that (B) is incorrect because the editorialist is not assuming those (political discussions that focus on the flaws of the nation's leaders) "will become more common."
When I negate the incorrect answer choice (D), Some in the nation have made the effort to critically examine the details of the nation's institutions and procedures, and apply it to the conclusion I have no reaction to it, so I think it has no affect on the argument, and thus is not an assumption that the editorialist has relied upon.
In regards to the argument, as a whole, I think the voting process for selecting the nation's leader is part of the nation's institutions and procedures that enable such people to attain positions of power. So, we(the people) are selecting leaders with flaws that a majority of us (can be argued against in certain cases) accepted, and now according to the stimulus, we are being distracted by that fact (acceptance). That can bring up the question of whom people have the distraction with, oneself or the nation's leaders.