US President Donald Trump has called the congressional impeachment investigation that may seek to remove him from office "a lynching".
In a tweet Mr Trump condemned the inquiry as "without due process or fairness or any legal rights".
Democrats may seek to impeach the Republican president by Christmas.
A racially loaded term in the US, lynching refers to historic extrajudicial executions by white mobs mainly against African Americans.
What's the reaction?
Mr Trump has repeatedly called the impeachment inquiry, as well as an earlier investigation into foreign meddling in the 2016 election, a "witch hunt".
But his likening of a process enshrined in the US constitution to racist killings provoked outrage among African-American lawmakers.
Congressman Jim Clyburn told CNN on Tuesday: "That is one word that no president ought to apply to himself."
"I've studied presidential history quite a bit and I don't know if we've ever seen anything quite like this."
"I'm a product of the South," the South Carolina Democrat added. "I know the history of that word. That is a word that we ought to be very, very careful about using."
Bobby Rush, an Illinois Democrat, tweeted to Mr Trump: "What the hell is wrong with you?"
"Do you know how many people who look like me have been lynched, since the inception of this country, by people who look like you."
He called on Mr Trump to delete the tweet.
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