Lamar White Jr., who runs a progressive publication called the Bayou Brief, tweeted the video, which he said shows Hyde-Smith with her arm around cattle rancher Colin Hutchinson, who had just praised her.
Republican Cindy Hyde-Smith is facing former congressman and former US agriculture secretary Mike Espy, a black Democrat, in a runoff November 27.
In August, President Trump endorsed Hyde-Smith over another Republican in Mississippi's State Senate, Chris McDaniel.
"Cindy Hyde-Smith's comments are reprehensible. We need leaders, not dividers, and her words show that she lacks the understanding and judgment to represent the people of our state", as documented by Huffington Post.
"They are hurtful to millions of Mississippians who are people of goodwill", Espy said.
"I put out a statement yesterday, and that's all I'm going to say about it", she said.
In the 10 second clip, Hyde-Smith can be heard speaking to a small group in front of a statue of Elvis Presley in Presley's hometown of Tupelo, Mississippi.
The former congressman noted that he sits on the board of directors at the Mississippi Civil Rights Museum and knows "that history very well".
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Espy said on CNN's "New Day" Monday morning that the comments were "disappointing" and reflected poorly on the state.
Mississippi's racial past is deeply mired with pain and ugliness.
Espy and Hyde-Smith had the top two vote tallies, each receiving about 41 per cent.
Another Republican from Mississippi, Trent Lott, lost his position as Senate majority leader in 2002 after saying at the 100th birthday party of SC U.S. Sen. According to the Equal Justice Initiative, 654 lynchings of black people were carried out within its borders, dramatically more than any other state.
Mississippi Senate contender Mike Espy... "She meant no offense by that statement". She will serve until the special election is resolved.
On Twitter, Johnson later said that Hyde-Smith's response to the controversy was "tone deaf and demonstrates disregard" for the state's history.
After numerous attempts Monday to get Hyde-Smith to elaborate, reporters directed questions to Gov. Phil Bryant, who stepped to the podium at Mississippi Republican headquarters and fielded questions as the senator stood beside him.
"There's no excuse to say what she said", White said of Hyde-Smith.