U.S. President Donald Trump is claiming a groundswell of African-American support in response to his comments denigrating Democratic Rep. Elijah Cummings and the congressman's majority-black Baltimore district, despite polling showing consistently negative numbers.

Speaking to reporters as he left the White House on Tuesday, Trump claimed the building had been flooded with thousands of letters, emails and phone calls thanking him for "getting involved" and exposing corruption.

"They really appreciate what I'm doing, and they've let me know it," said the Republican president. The White House did not immediately provide any evidence backing up Trump's claims.

Trump's comments came in response to fierce backlash against his earlier remarks lashing out at Cummings, the chairman of the House Oversight Committee, and calling his district a "disgusting, rat and rodent infested mess." Trump also is under fire for his ongoing attacks on four Democratic congresswomen of colour, who he tweeted should "go back" to their countries — even though three of the four were born in the United States and all are U.S. citizens.

But Trump on Tuesday nonetheless declared himself "the least racist person" in the world, despite his recent comments and racist tweets. And he said "African-American people love the job" he's doing, despite the fact that numerous polls have shown African-Americans are overwhelmingly negative in their assessments of his performance.

Approval among black Americans has hovered around 10 per cent over the course of Trump's presidency, according to Gallup polling, with eight per cent approving in June. And a new Quinnipiac University poll out Tuesday found that 80 per cent of registered African-American voters think Trump is racist, versus 11 per cent who think he's not.

I think I'm helping myself because I'm pointing out the tremendous corruption that's taking place in Baltimore and other Democratic-run cities. - U.S. President Donald Trump

Polling also suggests his recent attacks could hurt Trump with suburban voters — and especially women — whom he may need to win next year. Trump in recent days, however, has expressed to advisers on his re-election team that he believes his broadsides against the minority Democrats will help excite his core supporters.

Trump insisted Tuesday that there was "zero strategy" in his attacks and that he was only "pointing out facts," even as he argued they were benefiting him.

"I think I'm helping myself, because I'm pointing out the tremendous corruption that's taking place in Baltimore and other Democratic-run cities," Trump said, as he continued to hammer his criticism.

"Those people are living in hell in Baltimore," he said, adding he was open to some kind of unspecified federal involvement.

"If they ask," he said, "we will get involved."

Rep. Karen Bass, chair of the Congressional Black Caucus, accused Trump of exaggerating the economic gains that African-Americans have made since he took office. (Andrew Harnik/The Associated Press)

Economic gains exaggerated, legislator says

Vice-President Mike Pence, speaking to reporters in Columbus, Ohio, also defended Trump, pointing to the low black unemployment rate and criminal justice reform legislation that Trump signed into law last year.

"President Trump is someone who calls it like he sees it," said Pence. "President Trump believes in being able to say when things are not what they should be, to call on leadership, to call on state leadership, and say, 'You have to do better.'"

But Democratic Rep. Karen Bass and chair of the Congressional Black Caucus, accused Trump of exaggerating the economic gains that African-Americans have made since he took office and noted the continued racial gap.

"Currently, African-American unemployment remains double that of white Americans and the national average despite gains in the job market," she said.

Black unemployment did reach a record low during the Trump administration: 5.9 per cent in May 2018. It currently stands at six per cent. But many economists view the continued economic growth since the middle of 2009, when then-president Barack Obama was in office, as the primary explanation for hiring.