He also said that chants of "send her back" at a Trump rally on Wednesday were similar to chants he heard when trying to integrate a Baltimore pool in 1962.
"I was beaten and all kinds of rocks and bottles thrown at me. And the interesting thing is that I heard the same kind of chant, 'Go home, you don't belong here.' And they called us the N word over and over and over again," Cummings said in an interview with ABC News Chief Anchor George Stephanopoulos.
"What it does when Trump does these things, it brings up the same feelings that I had over 50 something years ago, and its very, very painful," Cummings said. "It's extremely divisive and I just don't think this is becoming of the president of the United States of America, the leader of an entire world."
Cummings added that his constituents have recently told him that they're "scared" of Trump.
"I've never in my total of 37 years in public service ever heard a constituent say that they were scared of their leader," he said.
When asked directly by Stephanopoulos, "Do you believe President Trump is a racist?" Cummings responded, "I believe he is -- yes, no doubt about it. And -- and I tried to give him the benefit of the doubt."
Last weekend, Trump tweeted an attack on Reps. Alexandria Ocasio-Cortez, Ilhan Omar, Ayanna Pressley and Rahsida Tlaib, saying "why don't they go back and help fix the totally broken and crime infested places from which they came. Then come back and show us how it's done."
Three of the four congresswomen were born in the U.S. and, the fourth, Omar, is a citizen who came to the U.S. as a refugee when she was a child.
The president stood by his remarks and then extended them to ask when the four congresswomen would apologize to the U.S., "for the foul language they have used, and the terrible things they have said." Then on Thursday, the day after a campaign rally in Greenville, North Carolina, where the crowd chanted, "send her back" about Omar, the president distanced himself from the chants.
ABC News correspondent Kyra Phillips asked Trump on Thursday if he thought the chants were racist and the president said no.
"You know what's racist to me? When someone goes out and says the horrible things about our country, the people of our country," he said.
In an interview following Cummings, Trump campaign adviser Mercedes Schlapp defended the president on "This Week" saying that he is not a racist.
In the past, Cummings has avoided calling Trump a racist outright, dodging a similar question on "This Week" in 2018. He said on Sunday that his point was to highlight the significance of Trump's remarks at this moment, saying "the president has to set the tone. He needs to be a role model."
"I know what it feels like to be at the other end of those kind of comments," Cummings said Sunday. "I see what's happening in our country with hate crimes going up, and we're getting more and more people being emboldened with making racist statements and treating people badly. And that's not the way we should be."
The president's tweets led to a resolution in the House of Representatives on Tuesday that formally condemned the remarks.
Trump tweeted again about the four freshmen Democratic congresswomen Sunday morning, known as "the squad," saying "I don't believe the four Congresswomen are capable of loving our Country."
Cummings took issue with the president's latest tweet, telling Stephanopoulos, "These are folks and women who love their country and they work very hard and they want to move us towards that more perfect union that our founding fathers talked about."
"So when you disagree with the president, suddenly you're a bad person," he added. "Our allegiance is not to the president. Our allegiance is to the Constitution of the United States of America and to the American people."
He also described the four congresswomen as brilliant and serves with all but Omar on the House Oversight Committee.
When asked if he was worried that Trump's strategy of focusing on them would work, or if their previous controversial statements were a distraction, Cummings said he was "not really" concerned, and chalked their controversies up to a lack of experience within the House of Representatives.
"Those kind of instances that you just mentioned do present a distraction at times. But I've realized that they are coming into a body that they've never served in before," Cummings said. "I've told them they can say the things they have to say but they got to say it in a different way. There's a way of saying things."