"It's unbelievable that we have a President of the United States who attacks American cities, who attacks Americans," the Vermont senator told CNN's Jake Tapper on "State of the Union," in an exclusive interview hosted from Detroit, Michigan.

Trump on Saturday suggested conditions in Cummings' district, which is majority black and includes parts of Baltimore, are "FAR WORSE and more dangerous" than those at the US-Mexico border. He continued his attacks into Sunday, tweeting that "Elijah Cummings has failed badly!" also taking aim at House Speaker Nancy Pelosi's San Francisco district. Pelosi previously condemned Trump's tweets on Cummings as racist attacks.

Cummings, the chairman of the House Oversight Committee, responded on Twitter Saturday by saying, "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."

Sanders called Cummings "one of the most decent and outstanding members of the House of Representatives."