The feud between President-elect Donald Trump and civil rights icon Rep. John Lewis spilled into the Sunday talk show circuit, with Vice President-elect Mike Pence saying he was “deeply disappointed” in Lewis and top Trump aide Reince Priebus saying Democrats need to “grow up.”

Lewis (D-Ga.) had told NBC News in remarks released Friday that he doesn’t view Trump as a “legitimate president.” He said he believes Russian hacking contributed to Trump’s election.

The back-and-forth comes ahead of the national holiday Monday celebrating the Rev. Martin Luther King Jr. and Trump’s inauguration Friday as the 45th president.

The 76-year-old Lewis, a 16-term congressman, fought for civil rights alongside King and was beaten in the 1965 march from Selma to Montgomery. He told NBC News’ “Meet the Press” that it will be “almost impossible” for him to work with Trump and urged fellow opponents in and out of government to organize.

“When you see something that is not right, not fair, not just, you have a moral obligation to do something,” Lewis said. “You cannot afford to be quiet or to be silent.”

Trump tweeted Saturday that Lewis is: “All talk, talk, talk — no action or results. Sad!”

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On Sunday, he tweeted a message of unity, “For many years our country has been divided, angry and untrusting. Many say it will never change, the hatred is too deep. IT WILL CHANGE!!!!”

Pence acknowledged Lewis’ contributions to U.S. history on “Fox News Sunday” and said it makes it all the more upsetting that the congressman would speak against Trump during what should be a peaceful transfer of power.

“I was deeply disappointed to see someone of his stature question the legitimacy of Donald Trump’s election as president and say he’s not attending the inauguration,” Pence said. “And I hope he reconsiders both positions.”

Several Democratic congressional members, including Reps. Yvette Clarke of Brooklyn, Adriano Espaillat of Manhattan and the Bronx, Jose Serrano of the Bronx and Nydia Velazquez of Brooklyn, Manhattan and Queens, said they stand with Lewis and won’t attend Trump’s inauguration.

Incoming White House Chief of Staff Reince Priebus criticized Lewis for appearing to contradict his convictions.

“For a person that is a champion of voter rights to question whether or not Donald Trump legitimately won an election or not, is an incredible position to take five days before an inauguration,” Priebus told ABC News’ “This Week.”

After host George Stephanopoulos noted that Trump for years had challenged President Barack Obama’s legitimacy by questioning his birthplace, Priebus said the outrage should not be on “old news.”

Priebus, speaking about the Democrats, said that Obama should “get his people in line and tell them to grow up and accept the fact that they lost the election.”

Trump tweeted Sunday that he believes more Democrats will come to support him as he begins to deliver results.

“The Democrats are most angry that so many Obama Democrats voted for me. With all of the jobs I am bringing back to our nation, that number will only get higher,” he wrote.