(CNN) ABC's decision to cancel Roseanne Barr's eponymous show following a racist comment she made about former Obama administration official Valerie Jarrett on Twitter was shocking for two reasons.

First, because it amounted to a TV network drawing a moral line in the sand -- insisting that no amount of money or ratings gave Roseanne the right to express views that ABC described in a statement as "abhorrent, repugnant and inconsistent with our values."

Second, because that decision to take a moral stand represents a stark contrast from the moral relativism preached by the president of the United States.

Donald Trump is different from anyone who has held the office before him in all sorts of ways. But, to my mind, the biggest -- and most critical -- difference between Trump and his predecessors is his total abdication of the concept of the president as a moral leader for the country and the world.

The examples of this sort of behavior are legion.

Trump impersonated a disabled reporter during a campaign speech and not only refused to apologize but insisted that attempts to say he was doing exactly what he was doing was evidence of the "fake news" media.

Asked by CNN's Jake Tapper about white supremacist David Duke's support for his candidacy, Trump played dumb. "Just so you understand, I don't know anything about David Duke, OK? " Trump told Tapper. Under pressure, Trump eventually disavowed Duke.

When then-Fox News anchor Bill O'Reilly -- in an interview during the 2017 Super Bowl -- noted that Russian President Vladimir Putin was a "killer,' Trump responded: "There are a lot of killers. We've got a lot of killers. What, do you think our country's so innocent?"

In the summer of 2017, Trump suggested there was blame "on many sides" of the white nationalist-provoked violence in Charlottesville, Virginia. "I watched those very closely, much more closely than you people watched it," Trump lectured reporters at the time. "And you have -- you had a group on one side that was bad, and you had a group on the other side that was also very violent, and nobody wants to say that, but I'll say it right now."

When multiple women came forward to allege that Alabama Senate candidate Roy Moore had sought relationships with them as teenagers -- and in several cases had forcibly grabbed or kissed them -- Trump at first threw his hands up, arguing that Moore denied the allegations, so who was to say what the real story actually was? Later, even though Moore offered a grand total of zero evidence that disproved the women's claims, Trump endorsed the Alabama Republican and held a campaign-style rally just across the Alabama border days before the vote.

After news broke that two ex-wives of then White House staff secretary Rob Porter had alleged abuse, Trump said this of Porter: "He says he's innocent and I think you have to remember that. He said very strongly yesterday that he's innocent but you'll have to talk to him about that."

There are lots and lots more examples just like these, but you get the point.

Trump simply does not see the world in terms of moral/immoral or right/wrong. He sees the world through one and only one lens: Friend/Foe. Or, understood slightly differently: Good for me/Bad for me.

Trump's refusal to condemn white nationalist violence in Charlottesville was born, in large part, out of his distaste for the political left. His refusal to condemn Moore's behavior was the direct result of his own experiences denying a series of allegations made against him by women during the 2016 campaign.

That is not an excuse for Trump. Far from it. Simply an attempt to explain.

The fact is that this is not a person who views his role in anything close to the same way that the other people who have held the same office did. While few of them were perfect -- and some like Richard Nixon and Bill Clinton failed in major ways -- they all believed in the basic idea that part of their job (and a large part of it) was to lead the country to the moral high ground. And that the best way to do that was through personal example. By taking the high road, by condemning hate and intolerance, they believed they showed the country the best of what we could be.

Trump's entire campaign and presidency has functioned as a rejection of past presidents -- and all that they believe. That included the idea that the president has some sort of broader responsibility to the body politic on morality.

Do whatever the hell you want to do as long as you win, was Trump's implicit message during the 2016 campaign. Who are these elites to judge you and your behavior? The world is a fight for survival. Might makes right. History is always written by the winners. And so on.

All of which brings me back to ABC's decision to fire Roseanne. There is little question that the comedian's show was, by Trumpian measures, a success. Its ratings were sky high.

Now, it's possible that this decision was motivated by advertisers' negative responses to the tweet. But as CNN reported , just two weeks ago, Barr was the centerpiece of ABC's upfront presentation to advertisers in New York.

ABC could have kept the show on the air, making the case that while they abhorred Barr's views, the show was about much more than her -- and was the launching point for lots of important societal conversations.

That would have all been PR speak for "the show rates extremely well and makes ABC lots of money," of course. But they could have gotten away with it.

ABC executives chose not to go down that path. Instead, they chose to make a very clear and public statement that doing the right thing sometimes (often? always?) matters more than making money.

What if Trump's reaction to the Roseanne firing was simply an echo of the ABC statement? Something like: Roseanne's Twitter statement is abhorrent, repugnant and inconsistent with American values, and I support ABC's decision to cancel her show.

The chances of Trump doing that are beyond miniscule, because of his total disdain for the idea of the presidency as a position of moral leadership. Rather, what I would expect from Trump is a tweet -- or a series of tweets -- using the cancellation of "Roseanne" to argue about the corrosive effect of political correctness and the toxic impact of Hollywood's liberalism.

Those are debates worth having. But that's not what Roseanne's tweet or ABC's decision to fire her are about. The issue here is whether racism, plainly expressed, should be condemned and penalized in this country.

ABC says yes. What does Donald Trump say?