Pay attention the next time you are on foot at an intersection waiting to cross with a group of other pedestrians.
Everyone stands restlessly looking at the orange hand of the "Don't Walk" sign. It's like they want to cross – there's no cross traffic preventing it – but some kind of social surface tension keeps the waiting pedestrians stuck to one another and to the curb. Is this light ever going to change? Finally whichever person is most impatient will start walking. Then, despite the "Don't Walk" signal that had them frozen in place a moment earlier, everyone follows him or her.
Psychologists and sociologists call this a permission effect, or describe the first individual to violate the (in this case minor, obviously) social taboo the "permission giver." Everyone wants to cross, since there's no effective reason not to. The "Don't Walk" sign is intended to keep the flow of traffic moving and to prevent pedestrians from getting hit; since there is no traffic, ignoring the sign will have no practical effect on anyone. But we know it's illegal anyway, and we know that we're supposed to obey signals like red lights and crossing signs regardless of whether they matter in our specific context. Then as soon as we see someone else throw caution to the wind, all those thoughts go out the window and we refocus on, "Well if he's gonna cross, I guess it's OK for all of us to cross."
It doesn't make any logical sense, but if you watch an intersection for a few minutes you'll observe this over and over. Everyone hesitates, one person transgresses, and everyone else follows. Clockwork.
Despite the pained, contorted efforts of old white men to explain how nothing that happens anywhere in the United States has anything to do with racism, anti-semitism, gay-bashing, misogyny, or anything else that has seen a resurgence in the political arena since 2015, we see evidence all around us, every day, that human beings are more likely to do something after they see someone else do it. This is neither a new nor an especially contentious finding. People, particularly more impressionable people like kids and the poorly educated, are more likely to say and do racist things after they watch someone else say and do racist things and – importantly – suffer no consequences. Steve Bannon rode a brief online career of rebranding anti-semitism for the digital age of journalism into the White House; other people will try to follow his lead. Success breeds imitation. As sure as the next few years will produce thousands of bad Chance the Rapper imitators, the internet will spawn a million wannabe Steve Bannons.
When we see racist or anti-semitic graffiti (or see Jewish property vandalized) the people making excuses for it may be right in a technical sense – a lot of it is probably the product of stupid kids, because vandalism tends to come from teenage boys. But the content of the vandalism is not a coincidence. It's a result of watching other people engage in a kind of social transgression (which teenage boys love, because it gets a rise out of people and brings them attention) without consequences. If they thought they would get arrested or go to prison for spraying swastikas on things, it would happen rarely. Now that they see that they can do it without consequences – or even with the potential of benefiting from it – there's no real reason not to do it. If the President says it, other people will naturally follow suit. If powerful people express ideas that were only recently frowned upon without any negative repercussions, others are going to follow their lead. It's not rocket science, but it's amazing the lengths to which people will go to deny it.