The US president had lashed out at senior Democratic congressman Elijah Cummings; a frequent critic of the administration’s immigration policy, its treatment of undocumented migrants and the conditions of detention centres along the US-Mexico border.
Mr Cummings, the chairman of the House Oversight Committee in congress, had recently questioned what he described as filthy conditions in the facilities.
His comments, combined with a Fox News segment that looked at the conditions in the democrat's congressional district of Baltimore, appeared to ignite Mr Trump's tirade.
The president described Mr Cummings as a “brutal bully shouting and screaming at the great men & women of Border Patrol about conditions at the Southern Border, when actually his Baltimore district is FAR WORSE and more dangerous".
“His Baltimore district ... is a disgusting, rat and rodent infested mess," said Mr Trump on Twitter.
Blackwell, 38, was born and raised in Baltimore and was clearly personally affronted by the president’s latest tirade - which he said was part of a larger pattern of language used by the president when referring to people of colour and areas where they live.
During an address to camera, he drew attention to the context within which Mr Trump tended to use the word "infested".
“Infested. That’s usually reserved for references to rodents and insects, but we’ve seen the president invoke infestation to criticise lawmakers before. You see a pattern here?” said Blackwell.
“Donald Trump has tweeted more than 43,000 times, he’s insulted thousands of people many different types of people, but when he tweets about infestation it’s about black and brown people.”
He reminded his audience of another of Mr Trump’s tirades against people from minority groups.
“Just two weeks ago President Trump attacked four minority congresswomen. 'Why don't they go back to the totally broken and crime-infested places from which they came?' Reminder, three of them were born here; all of them are American.”
The four democratic congresswomen, Ayanna Pressley, Alexandria Ocasio-Cortez, Ilhan Omar and Rashida Tlaib, are all US citizens.
Three of them were born in the United States, while Ilhan Omar came to the country as a child refugee from Somalia.
After attempting compose himself, the TV presenter eventually managed to continue talking but appeared to be choking back tears as he recalled Mr Trump’s description of his hometown.
“The president says about Congressman Cummings’ district that no human would want to live there," he said.
“You know who did Mr President? I did. From the day I was brought home from the hospital to the day I left for college and a lot of people I care about still do.
“There are challenges no doubt. But people are proud of their community. I don’t want to sound self-righteous but people get up and go to work there.
“They care for their families there. They love their children who pledge allegiance to the flag just like people who live in districts of congressmen who support you sir.
“They are Americans too.”
Mr Trump’s latest tirade saw social media users describe him as "openly racist" and "a brutal bully" and an embarrassment to the country.
In response to Mr Trump, Mr Cummings said on Twitter: “Mr. President, I go home to my district daily. Each morning, I wake up, and I go and fight for my neighbors. It is my constitutional duty to conduct oversight of the Executive Branch. But, it is my moral duty to fight for my constituents.”
ProRepublica reporter Alec MacGillis suggested on Twitter that many of the district's problems were due to the president’s administration and the poorly-maintained apartments owned by his son-in-law Jared Kushner.
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