US President Donald Trump has called the congressional impeachment investigation that may seek to remove him from office “a lynching”.
Mr Trump condemned the inquiry in a tweet 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.
White House spokesman Hogan Gidley told reporters on Tuesday that Mr Trump did not mean to be racially insensitive.
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.