Sen. Cindy Hyde-Smith, R-Miss., attends her swearing-in ceremony in the Capitol's Old Senate Chamber after being sworn in on the Senate floor on April 9, 2018.

Voters in Mississippi on Tuesday will decide a U.S. Senate special election runoff marked by racial controversy and capped by a last-minute visit by President Donald Trump to shore up the beleaguered Republican incumbent.

Senator Cindy Hyde-Smith, a white former state lawmaker who was appointed to the seat in April, is still favored over black Democrat Mike Espy in the reliably Republican state, which has not sent a Democrat to the U.S. Senate since 1982.

But she has been engulfed in a political storm since a video surfaced showing her praising a supporter at a Nov. 2 public event by saying: "If he invited me to a public hanging, I'd be on the front row."

The comment caused an uproar in Mississippi, a deep South state with a history of racism and violence against blacks, including lynchings. Several businesses, including giant retailer Walmart, demanded that she return their donations.

Hyde-Smith was also shown on another video joking about suppressing liberal student votes, and photographs have surfaced of her posing with Confederate artifacts in 2014.

Espy, a former congressman and U.S. agriculture secretary, gained new momentum from the furor in a state where 38 percent of residents are African-American.

"She is still the front-runner, but she is a wounded front-runner. She's not the sure thing she was a few weeks ago," said Nathan Shrader, a political science professor at Millsaps College in Jackson, the state's biggest city.

Hyde-Smith, who initially refused to apologize for the hanging remark, said last week she was sorry "for anyone that was offended" and accused Espy of twisting her words for political gain.