In American poltical discourse, legitimate opinions are represented by two different, but equally important groups: Democrats and Republicans. Political debate, as it is commonly understood, just is the dispute between the two parties. This is why it is possible to implement policies using American political institutions while at the same time “putting the politics aside” — because politics is defined as a dispute between Democrats and Republicans, a bipartisan consensus is no longer political. And since American political discourse lives in mortal fear of political division — a condition that is taken to be unnatural and illegitimate — bipartisan consensus is the most highly desired outcome.
Failing that, of course, political commentators and journalists reflexively return to the idea that the two parties, which should agree in all things, are at least in agreement as to their faults. If “both sides” were not of the same moral caliber, evincing the same degree of corruption, dishonesty, ignorance, and other undesirable traits, then that would call into question the legitimacy of one of the two sides and forever close down the possibility of bipartisan consensus. It would open up the possibility of permanent political division, rather than momentary disagreement between people of good faith whose different starting points ultimately enrich our great national dialogue, etc., etc., etc.
Within this system, neither political party can be wrong. Individual outliers within a given political party can be wrong — indeed, they can make statements and propose policies so ridiculous that, in the eyes of respectable discourse, all citizens of good faith should put the partisanship aside in order to vote against that person. Most often, those outliers are painted as outsider populists who abuse the primary system to subvert the real spirit of their party. It is even possible for the party as such to err in the short term, as the Republicans may well be doing by nominating Trump and pushing through a scary right-wing platform. Yet in the long run, each party is definitionally in the right, insofar as the Democrats and Republicans represent the only two legitimate options within the American political field. Trump will have been an overreach if the Republicans decide that he was — if they double down, Trumpism will turn out to be legitimate Republicanism.
It goes without saying that such a system is gameable, that the Republicans figured this out long ago, and that the Democrats believe so deeply in respectability that they are forced to play along with the charade of two equally legitimate “sides” — because to do otherwise would be to open up the prospect of a permanent and unbridgeable political division, which may well be the one sole taboo of American political discourse.