(CNN) In the umpteenth scandalous moment of his reign, the President tweeted that four Congresswomen -- three homegrown Americans and one who became a citizen of the United States at age 17 -- should "go back and help fix the totally broken and crime infested places from which they came." The racism in this attack is appalling, but it is not the only form of deviance on display.

That would be the suggestion, which he later amplified, that Donald Trump has anointed himself the judge of who belongs in America and who does not.

This should strike fear in every heart because it means that the most powerful person in the country -- with a large cohort of supporters ready to follow him anywhere -- has begun to sort and separate us from each other. In this moment he finds these four elected public servants unacceptable, but who's to say what he'll think about any of us tomorrow, should we dare to disagree with or challenge him?

This is a serious question, with terrifying implications, that voters need to examine before they cast their vote in the 2020 election.

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Consider that as social beings who depend on our families, our communities, and yes, our country for our identity and well-being, few things are more upsetting than the prospect of being rejected and cast out. Shunning is so painful that most of us will go to great lengths to avoid it. Religious groups that use the threat of excommunication to keep people in line -- "in the fold" --understand this powerful dynamic and so do bullies who make a show of victimizing one kid in order to dominate everyone on the playground.