(CNN) On Thursday morning, the President of the United States sent a tweet to his 60+ million followers blasting a 16-year-old girl with Asperger's syndrome who has rallied efforts at fighting climate change around the globe.

"Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend!" Trump wrote of teenage climate crisis activist Greta Thunberg. "Chill Greta, Chill!"

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This isn't the first time Trump has gone after Thunberg. "She seems like a very happy young girl looking forward to a bright and wonderful future," Trump sarcastically tweeted following Thunberg's speech in front of the United Nations General Assembly earlier this fall. "So nice to see!"

Sadly, Trump's response is predictable in the wake of the Swedish climate activist being named as Time's Person of the Year over him. Trump is a bully. And he has shown time and again that he has no qualms about bullying anyone and everyone. Let's not forget that he poked fun at Carly Fiorina's looks when she was competing with him for the Republican nomination during the 2016 campaign. And in that same campaign, Trump mocked a New York Times reporter by crudely mimicking his physical disability . So that the president of the United States would tell a 16-year-old with Asperger's -- a condition most distinguished by difficulty with social interactions -- to make some friends and, basically, relax, fits nicely into that pattern of behavior.

Thunberg responded by changing her Twitter bio to mock the President's words, referring to herself as: "A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend." Thunberg has been open about her neurological difference, acknowledging both the struggles she's had and calling it a " superpower " when it comes to her activism.

Trump is Trump. He has never behaved in any other way than this. Which doesn't excuse Trump's behavior. But it makes surprise that he acts this way impossible.

What's truly troubling -- and what makes me genuinely mad -- about all of this is that we won't hear condemnation from supporters of Trump (in elected office and out) for this absolutely appalling behavior.

Why? Because, at this moment in American political history, the party you identify with trumps -- ahem -- everything else including common decency.

Because common decency would dictate that, as a society, we don't condone an adult bullying a 16-year-old girl online. Because we know it's wrong. Because we know if we had a daughter, we wouldn't want her to be bullied by an adult. Much less an adult man. Much less one who is the President of the United States.

That is not a partisan position. It is a moral one. It is a common sense one. Don't believe me? Listen to first lady Melania Trump

"In today's global society, social media is an inevitable part of our children's daily lives. It can be used in many positive ways, but can also be destructive and harmful when used incorrectly. This is why 'Be Best' chooses to focus on the importance of teaching our next generation how to conduct themselves safely and in a positive manner in an online setting."

Agreed! The dangers of online bullying to our kids are real and only getting worse. That's something on which we can and should all agree!

And yet, when the single most powerful person in the country bullies a 16-year-old girl with Asperger's, there's no reasonable expectation that everyone -- Republican, Democrat and people who could care less about politics -- will roundly condemn this behavior.

Which, what the hell? Our common humanity should dictate that we don't let the President -- or ANY adult -- bully a kid, right? RIGHT? RIGHT.

That we have lost that memory of our common humanity is hugely worrisome. And may well be the lasting legacy of Trump's time in office.