Hours before sheltering in the Capitol, the first-term lawmaker was at the "Stop the Steal" rally encouraging Trump supporters to reject the results of the election.
Madison Cawthorn of North Carolina made the comments just weeks before a mob attacked the U.S. Capitol.
During the 2020 election, Democrats retained their majority in the House of Representatives.
Cawthorn, who is 25, won the North Carolina seat once held by White House Chief of Staff Mark Meadows.
“It just really personally saddens me that somebody who is so clearly racist is a nominee of a major party," the U.S. senator from New Jersey said.
Madison Cawthorn, 25, had said that visiting the Eagle's Nest was on his "bucket list" in Instagram photos from 2017.