President-elect Donald Trump has begun a long holiday weekend that honours slain black civil rights leader Martin Luther King Jr by attacking another rights activist and politician who has questioned Trump's legitimacy.
Georgia Democrat John Lewis told NBC's Meet the Press he thought hacking by Russians had helped Republican Trump get elected in November.
Lewis said he does not plan to attend Trump's Jan. 20 inauguration, the first time he would miss such an event since being elected to the House in 1986.
On Saturday Trump tweeted that Lewis had falsely complained about the election results and instead "should spend more time on fixing and helping his district, which is in horrible shape and falling apart (not to mention crime infested)".
"All talk, talk, talk - no action or results. Sad!" Trump tweeted.
The 76-year-old Lewis, who has been a civil rights leader for more than half a century, was beaten by police during a march he helped lead in 1965 in Selma, Alabama, drawing attention to hurdles for blacks to vote and protested alongside King that day and on other occasions.
"I believe in forgiveness," Lewis said in the NBC segment about Trump.
"I believe in trying to work with people.
"It's going to be very difficult. I don't see this president-elect as a legitimate president."
At least 10 other Democratic politicians have also said they plan to skip the inauguration, while several of Trump's fellow Republicans also criticised his tirade against Lewis.
Michael Steele, who served as the first black chairman of the Republican National Committee until 2011, said Trump's tweets were unfortunate.
"John Lewis has a walk that very few people in this country, least of all Donald Trump, have ever walked, so you have to respect that," Steele said on MSNBC.
And Senator Ben Sasse of Nebraska tweeted that "John Lewis and his 'talk' have changed the world."
Conservative critic Bill Kristol tweeted "It's telling, I'm afraid, that Donald Trump treats (Russian President) Vladimir Putin with more respect than he does John Lewis."
Trump's comments about Lewis came ahead of an anti-Trump march of about 2000 people in Washington headed by the Reverend Al Sharpton, which kicked off a week of rallies planned by dozens of groups against the president-elect before, during and after his January 20 inauguration.
DisruptJ20, which is working with Black Lives Matter and other protest groups, say they plan to disrupt balls celebrating the inauguration in Washington.
