JACKSON, Miss.  As a Democrat running for the Senate in the Republican stronghold of Mississippi, Ronnie Musgrove faces a challenge that was summed up in the angry words of a middle-aged white voter doing business at the courthouse here this week.

“I wouldn’t vote for him if he was the last man on earth,” said Roger Case, an employee of a fire-extinguisher company, as Mr. Musgrove campaigned a few yards away. Blacks in the courthouse beamed at Mr. Musgrove, a lanky former governor; whites, mostly, looked the other way.

Mississippi has not elected a Democrat to an open Senate seat since 1947, but that is not stopping the Democratic Party from heavily financing a major effort here, one of a handful of states  including North Carolina, Minnesota and possibly Oregon  it thinks it can pull from Republicans this fall in a reach for the filibuster-proof 60-vote majority.

More than $3 million has been spent by the Democratic Senatorial Campaign Committee to support Mr. Musgrove; turn on a television here and the candidates can be found flailing at each other’s ethics, morals and probity in what local analysts say is a never-seen-before barrage of negative advertisements.