Romney being a racist was not a major (or even minor) theme of Obama's campaign. I don't think you can really be suggesting that alleged racism on the part of the Republican candidate was as big an issue in the previous election as in the present one (where the Republican candidate made widely publicized explicitly racist statements).
I agree that the "$republican is literally hitler", "$republican is racist", etc, is more hysterical this time around. I attribute that to Trump being blatantly on the wrong side of the culture war [1].
I'm just saying that "XXX republican is racist" has lost it's meaning due to overuse. The boy has cried "hitler" about Bush, Romney, etc, and the villagers will no longer come running.
I think this is wrong in two respects. First, the statement has not lost its meaning but only its effect. Second, the claim that Bush and Romney were racists was not a major strand of political discourse. People talked about Republican policies rooted in racism, but that is a very different thing from having a presidential candidate who is himself, on a personal level, a racist.
Bill Maher is no genius, but even before the election he had already identified this lack of credibility, the umpteenth time some random Republican is deemed beyond the pale:
There are always people on each side making outrageous allegations about each candidate. The question of whether Romney was a racist was not a major issue in the previous campaign.
http://www.dailykos.com/story/2012/8/27/1124649/-Romney-Goes...
http://nymag.com/daily/intelligencer/2012/07/romney-accused-...
https://www.buzzfeed.com/mckaycoppins/romney-faces-challenge...
https://thinkprogress.org/romney-dog-whistle-obamas-philosop...