I doubt that Carson would have won as Bush won by 30 points and control of the Senate was an issue (I didn’t doubt we would gain but going in with only 51 it was an issue). That’s a lot of crossover votes, no matter how “rovian” Humphreys was.
I was following the race and Carson led in the polls and Humphreys was a subpar candidate (and it was even shaping up to be an retro-style race where the Democrat would carry the rural areas and the Republican the urban). Coburn neutralized Carson by coming from the same rural district. Given that Brad Henry had similarly upset the GOP preference of Steve Largent two years earlier (a good GOP year), it was too risky a chance.
The same problem arose in Colorado with the Rovian drafting of Pete Coors, who was the premier execrable candidate of that cycle (and a similar excuse was that Dubya would carry the state and so would Coors, and that didn’t happen). Had Bob Schaffer been the nominee, he’d have defeated Ken Salazar and would be the senior Senator there today.