At a 2020 campaign rally in New Hampshire last night, a protest broke out. A Trump supporter sought to remove the protesters.

And as that was happening, the President of the United States yelled this into the microphone: "That guy's got a serious weight problem. Go home. Start exercising. Get him out of here please.

"Got a bigger problem than I do. Got a bigger problem than all of us. Now he goes home and his mom says, 'What the hell have you just done?'"

US President Donald Trump has mocked an supporter he mistook for a protester at a 2020 campaign rally, claiming he has a "serious weight problem" and advising him to "start exercising". (AP)

For anyone familiar with Mr Trump's rhetoric, it's clear he misunderstood the situation. He regularly taunts protesters at his rallies by telling them to run home to their moms.

Mr Trump clearly thought the man escorting the protesters out was a protester himself, not a Trump supporter.

Briefed on his mistake after the rally, Mr Trump called the man and left a message thanking him for his support, according to CNN White House reporter Kaitlan Collins. But, as Kaitlan noted via Twitter:

"Trump did not apologise, a White House official tells me. He phoned the supporter, left him a message thanking him for his support, but did not use the words 'sorry' or 'apologise'."

No, of course he didn't.

Briefed on his mistake after the rally, Mr Trump called the man and left a message thanking him for his support, according to CNN White House reporter Kaitlan Collins. (AP)

Here are the things I find remarkable about all this:

1) We have a President who thinks fat-shaming someone in front of thousands of people is a totally acceptable thing to do

2) The crowd laughed and applauded when Mr Trump made the comment about the man's weight

3) Mr Trump only decided to reach out to the man when informed he was a supporter

4) The White House went out of its way to make clear that Mr Trump did not apologise to the man

Boy oh boy. What a commentary on this moment in time in American politics and culture.

Mr Trump mainstreamed bullying as a political tactic during the 2016 primary campaign, so no one should be surprised that, as President, he talks like this.

But it does serve as yet another reminder that the biggest difference between Mr Trump and those who have held the office before him is that he absolutely rejects the idea of the presidency as a beacon of moral leadership.

Mr Trump mainstreamed bullying as a political tactic during the 2016 primary campaign, so no one should be surprised that, as President, he talks like this. (AP)

His reaction to the white nationalist march in Charlottesville, Virginia, proved that. His mocking of a disabled reporter on the campaign trail in 2016 proved it. His comments about immigrants from "shithole countries" proved it.

His insistence that Mexico was sending rapists and criminals to the United States proved it. His decision to called Baltimore "rat-infested" proved it. And on and on it goes.

What Mr Trump has done is not only ignore the idea that a president of the United States should take the high road, but also made a mockery of the very idea.

He champions his low-roaded mindset every chance he gets, wearing it as a badge of honor to his supporters.

To Mr Trump, and those who laugh and jeer right along with him, his willingness to break with standards of accepted behavior speaks to how radical a change he is to a staid and broken political system and culture.