NAACP President Cornell William Brooks is calling on President-elect Donald Trump to apologize for criticizing Rep. John Lewis (D-Ga.), a civil rights icon.

In a Saturday tweet, Brooks said Trump’s remarks “demeaned Americans” and the rights Lewis has fought for throughout his life.

By disrespecting @repjohnlewis, @realDonaldTrump dishonored Lewis' sacrifice & demeaned Americans & the rights, he nearly died 4. Apologize. pic.twitter.com/kFBSfz2wyv — Cornell Wm. Brooks (@CornellWBrooks) January 14, 2017

In tweets posted Saturday morning, Trump said Lewis was “all talk, talk, talk - no action or results.”

Lewis is famous as a civil rights leader who helped organize protests and events to raise awareness about voting rights. Police beat him and other voting rights activists in 1965 as they crossed the Edmund Pettus Bridge in Selma, Alabama, on what is now known as “Bloody Sunday.”

Trump’s tweets appear to be a response to comments Lewis made to NBC News on Friday, questioning the legitimacy of Trump’s presidency.

“I think the Russians participated in helping this man get elected and they have destroyed the candidacy of Hillary Clinton,” Lewis said.