AFTER Election Day, “This is not normal” became a rallying cry for Donald Trump’s opponents: Harry Reid warned against press coverage that normalized the president-elect; a John Oliver monologue about Trump being abnormal won 14 million YouTube views; THIS IS NOT NORMAL T-shirts popped up around the country. But in July, after critics opined that his bullying tweets were “not normal,” Trump tweeted back that his social-media usage, far from deviant, was simply “MODERN DAY PRESIDENTIAL.” Maybe he’s hit on an uncomfortable truth: Even abhorrent things can become standard. Could his behavior become normal?
The answer depends in part on what we mean by normal. Recent research suggests that our sense of what’s normal reflects not only our belief about what’s average, but also our sense of what’s ideal. In one experiment, subjects said that three hours was a normal amount of TV to watch each day—in between the 2.3 hours they described as ideal and the four hours they said was average.  What people consider normal or typical can also depend on how much they know. According to an earlier study, non-experts were likely to call a tree typical if it was familiar to them; tree experts were likely to call a tree typical if it was prescriptively ideal. 
Complicating matters, our sense of what’s ideal can be fickle. Children, who by age 3 have ideas about what is normal behavior,  are prone to seeing an instance of a random behavior—someone taking items out of a bag in a certain way, say—as exemplifying a norm, even without any prompting.  Among adults, too, conventions can emerge with surprising speed.A University of Pennsylvania study asked members of a social network to look at images of adults and name them. After each participant shared his or her suggested name with just a few others in the group, the entire network quickly reached consensus.  This helps explain how names that were uncommon 20 years ago, like Aiden, can become, well, normal.
Norms can also shift quickly on more disturbing matters. In one study, a group of women was shown a movie that presented stalking as romantic. For some, the romantic portrayal “normalized” the behavior; these subjects later registered a more permissive attitude toward stalking.  Similarly, a recent working paper found that when people were told that a xenophobic opinion they disagreed with was in fact a popular view, they were less likely to judge a person who publicly subscribed to it. 
More than simply destigmatizing the fringe, exposure to extreme opinions can change one’s sense of normality. When researchers presented more than 1,000 subjects with either radically conservative or radically liberal policy options—for example, ban immigration, or don’t limit it at all—their sense of what a centrist position was shifted toward that extreme. 
So yes, norms can shift to accommodate deviance. Of course, if Trump truly wants to be seen as “modern day” normal, a simpler route would be for him to move toward existing norms, instead of waiting for the norms to come to him.