It is beyond gone for them in presidential races, but the right Democrat (one who is perceived as an outsider or moderate or populist or whatever) could easily win a Senate or gubernatorial race there. Missouri politics is quite awful, honestly. It is easily my least favorite "red" state.
What makes it different for a national candidate, if they'd vote for the exact same person on a local level? Trust?
I think it is the level of responsibility, as well as the difference between someone being 1 of 50 (a governor) or 1 of 100 (a Senator) and being the one and only (a President). Tennesseeans voted for Al Gore for Senator, when he was 1 of 100--balanced by Senators of the other party as well as those that differed regionally and ideologically. But when it came time to vote to make Al Gore the chief decision maker of the land, Tennesseeans (by 51%-47%) said No.
Also, for some reason, I trust local Democrats much more readily than Democrats from elsewhere, more so than for Republicans. I don't think my reaction is atypical. It is well-known that the South mostly elected Democrats to the House and Senate well into the 1990s, long after it had swung to the GOP at the Presidential level. Similarly for Macomb County: the GOP didn't even have a presence to speak of at the county level until well into the 1980s, Congressmen Dennis Hertel and David Bonior regularly trounced their GOP opponents (the GOP didn't even bother putting up a challenger to Hertel in 1982). Still, Macomb voted 2-1 Reagan in '84 and nearly 2-1 Nixon in '72.