President Trump heads to Baltimore, a city he called a 'rodent infested mess'

He also attacked Rep. Elijah Cummings, the city's African American congressman.

The president was scheduled to address House Republicans as part of their three-day retreat at a hotel in downtown Baltimore, near the Inner Harbor. Protests, including a “No Racists in Our Streets" rally, were planned against a visit by the president, who has called the city the “worst in the USA” and a place “no human being would want to live.”

Earlier, protesters placed a giant rat-shaped balloon with a Trump head near where the president would be stopping.

Trump’s feud with Baltimore was sparked – seemingly out of the blue – on Twitter in what appeared to be retaliation against investigations against him launched by the House Oversight Committee and its Democratic chairman, Rep. Elijah Cummings. Cummings’ district, which is mostly African American, covers part of Baltimore and is just a few blocks from where Trump is speaking.

Since late July, the president has lobbed attacks against Cummings and the city of Baltimore, a city of over 600,000.

“Rep, Elijah Cummings has been 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 district is considered the Worst in the USA,” Trump tweeted.

“As proven last week during a Congressional tour, the Border is clean, efficient & well run, just very crowded. Cumming District is a disgusting, rat and rodent infested mess. If he spent more time in Baltimore, maybe he could help clean up this very dangerous & filthy place.”

Cummings, who has served the area for decades, responded by saying he continues to work for his district.

“Mr. President, I go home to my district daily,” he said. “It is my constitutional duty to conduct oversight of the Executive Branch. But, it is my moral duty to fight for my constituents.”

Maryland's GOP governor, Larry Hogan, called Trump’s comments “ outrageous and inappropriate.”

"Washington is just completely consumed with, with angry and divisive politics, the divisiveness and dysfunction. And then 14 hours later we get this tweet that sets off another fire storm of angry tweets back and forth."

The city of Baltimore has struggled for years with crime, poverty and issues with housing. In 2018, there were a record number of homicides in Baltimore, with 309 killed according to the Baltimore Police Department. But some have pointed to issues with developers and local landlords, including Trump’s son-in-law Jared Kushner whose family real estate firm owns apartments and townhomes in Baltimore. In 2017, the county reported some 200 code violations in apartments owned by the Kushner family in one year alone.

Trump’s only African American Cabinet member, Housing Secretary Ben Carson, is from Baltimore and acknowledged the city’s problems.

"You know, it's sort of like if you have a patient who has cancer," Carson said of Baltimore. "You can dress them up and put a nice suit on them, and you can try to ignore it. But that cancer is going to have a devastating effect. You have to be willing to address that issue if you're ever going to solve it."

At the beginning of August, Cummings invited Trump to come visit.

“I want President Trump to visit Baltimore,” he said. “My God, I want him to come, I’ll ride with him for hours if I have to.”

The White House does not have any plans for the president to tour the city before or after his speaking engagement.

ABC News' Anne Flaherty contributed to this report.