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“It’s polarizing, it’s divisive and I think it’s an old school strategy that may pay off in the short term,” said Donna Brazile, a former Democratic National Committee chairwoman. “Long term it’s damaging to our country, it’s tearing us apart.”

Outside the White House, Mr. Trump's supporters are echoing his sentiments about Baltimore and Mr. Cummings. Senator Rick Scott of Florida condemned the congressman in a Sunday interview with NBC News. And Darrell Scott, a Cleveland minister who was a co-founder of the 2016 Trump campaign’s diversity coalition, said Mr. Trump is correct about living conditions in Baltimore.

“We can’t say just because someone was a civil rights activist and marched 50 years ago that that immunizes them against any criticism,” Mr. Scott said of Mr. Cummings. “He shouldn’t walk it back. There’s nothing to walk back.’’

The president showed no signs of retreating Monday, unleashing new criticism against Mr. Sharpton, continuing his attacks on Mr. Cummings and gathering African-American supporters at the White House. Late Monday, he laced into Mr. Cummings and Baltimore again, saying money funneled to the city had been “stolen or wasted.”

While the president presses his attacks with few repercussions, Democrats are left in the familiar position of debating the best way to respond: Attack him? Ignore him? Pivot to issues like health care?

Polling conducted before last year’s midterm elections by the Democratic super PAC Priorities USA found that mentioning Mr. Trump depressed enthusiasm among African Americans, especially younger ones, who viewed his 2016 victory as proof of a political system stacked against them.

With that in mind, Democrats who carried the party to victory in the House and flipped seven governor’s mansions did so largely by ignoring Trump in their campaigns, treating the president as background music they could sing along to without addressing him directly.