Jean Carnahan was running to replace her deceased hubby. Mel Carnahan was leading the race for Senate and Jean just like Claire McCaskill had populist appeal
This. Missouri was still competitive then and Democrats had an unexpectedly great year in Senate elections which helped push Carnahan over the top. The days leading up to the election were full of gauzy tributes and memorials with people like Sheryl Crow. Ashcroft was polarizing and of course Democrats didn’t want to give up their chance to vote against him because of a horrible accident. The combination of core Democratic support, a good year for Dems in general and the feel-good appeal to “don’t let the light go out” which Ashcroft couldn’t respond to effectively added up to a win.