Donald Trump has caused outrage after comparing the impeachment inquiry Democrats have brought against him to "a lynching".
Lynchings, which were often hangings, were used mostly by whites against black people. They happened mainly in the southern United States, starting in the late 19th century amid rising racial tensions.
"That is a word that we ought to be very, very careful about using," said the highest-ranking African American politician in Congress, Democratic Representative James Clyburn.
So some day, if a Democrat becomes President and the Republicans win the House, even by a tiny margin, they can impeach the President, without due process or fairness or any legal rights. All Republicans must remember what they are witnessing here - a lynching. But we will WIN!— Donald J. Trump (@realDonaldTrump) October 22, 2019
"That is one word no president ought to apply to himself," Mr Clyburn added.
Representative Bobby Rush, who is also black, called on Mr Trump to delete his Twitter comment.
"No sir! No," tweeted Senator Doug Jones. "This is NOT a lynching, and shame on you for invoking such a horrific act that was used as a weapon to terrorise and murder African Americans."
Democrats, who have a majority in the House of Representatives, are pushing for Mr Trump to be impeached for asking Ukraine president Volodomyr Zelenskiy to look into 2020 presidential hopeful Joe Biden and his son, Hunter, who was on the board of a Ukrainian oil company.
Mr Trump tweeted: "So some day, if a Democrat becomes President and the Republicans win the House, even by a tiny margin, they can impeach the President, without due process or fairness or any legal rights. All Republicans must remember what they are witnessing here - a lynching. But we will WIN!"
Defending the president, Republican senator Lindsey Graham said Mr Trump's description was "pretty well accurate".
He described the impeachment campaign as a "sham" and a "joke", because the president does not know the identity of his accuser, and the process is happening in private.
"This is a lynching in every sense," Mr Graham said.
The Senate's only black Republican, Tim Scott, said the impeachment process was "the closest thing (to) a political death row trial", but added: "I wouldn't use the word lynching."
White House spokesman Hogan Gidley said the president was trying to show how he had been "attacked" by the media since he took office.
"The president's not comparing what's happened to him with one of our darkest moments in American history," Mr Gidley said.