Cindy Hyde-Smith, who is white, and Democrat Mike Espy, who is black.
The vote tightened after Ms Hyde-Smith was recorded telling a supporter she would happily attend a public hanging.
State officials said the nooses were accompanied by handwritten signs mentioning lynchings and Tuesday's special Senate runoff, which has drawn attention to Mississippi's history of racially motivated violence. Hyde-Smith ultimately apologized but not before Espy responded during a debate calling the comments, "what's in her heart".
Espy denied the charge and said, "We all know what came out of your mouth". MS has a long history of racially-motivated lynchings of black people and of suppressing voters. There were 4,743 lynchings in the United States between 1882 and 1968 and nearly three-quarters of the victims were black, according to NAACP. It says MS had 581 lynching during that time, the highest number in any state.
Donald Trump praised Ms Hyde-Smith as he headed to Mississippi to lead two rallies for the senator.
The runoff Senate victor will serve the final two years of now-retired Sen.
Manchester United's Victor Lindelof misses training ahead of Young Boys clash
I don't think it's proactive for the club. "Everyone in the changing room is a fighter and we want the best for the team and the club".
Hall: Hyde-Smith. She's had a rough three weeks - largely self-inflicted - but I think most of it turns out to be political flesh wounds.
"She produces like few produce", Trump said. And sure enough, Tuesday's runoff election isn't on everyone's radar here.
Jonathan Winburn, a professor of USA politics and public policy at the University of MS, said he expects the race to be "more competitive than the norm in MS", but said he's not convinced the Hyde-Smith controversy will be enough to deliver her the same fate as Moore. The Republican candidate also and pushed for a revisionist review of the Civil War in 2007 when she was the state's senator.
He was endorsed by former Vice President Joe Biden and three Democrats who are potential 2020 presidential candidates - former Massachusetts Governor Deval Patrick and Senators Kamala Harris of California and Cory Booker of New Jersey - travelled to MS to campaign for him.
"I love Mississippi and I love being with you in Mississippi", Trump told the crowd at the beginning of his speech.