Georgia Rep. John Lewis' comments about President-elect Trump were "uncalled for," Democratic Sen. Joe Manchin said Sunday.

"I've got the utmost respect for Congressman Lewis. He's an icon, if you will," Manchin told CBS' John Dickerson. "I just think that was uncalled for. I just wish that rhetoric would tone down from both back and forth."

Lewis had said last week he doesn't view Trump as a "legitimate" president, nor does he look forward to working with the president-elect once he enters office.

The "bickering going on back and forth" between Lewis and Trump makes the U.S. look weaker to its allies, Manchin said.

"We're bigger than this, and we're going to show them we're not going to change and not going to alter how we work and function as Congress, as a government and the United States of America," he added, describing such bickering as "non-productive."

Lewis and Trump have taken repeated swipes at each other since the Georgia Democrat first said he would not attend the president-elect's inauguration next week.

"Congressman John Lewis should finally focus on the burning and crime infested inner-cities of the U.S. I can use all the help I can get!" Trump tweeted on Saturday.

Manchin has developed a close relationship with the incoming Republican president, despite their partisan differences. The conservative West Virginia Democrat skipped a meeting between his colleagues and President Obama last week for a sit-down with Vice President-elect Mike Pence instead.