I dono't know anything about Governor but I do know the recent history of Republican Presidents who had primary opposition. Defeat in the General election.
Gerald for lost to Carter and Bush lost to Clinton. Not a real good record of success.
The general thought is that it demonstrats the parties general dislike of the sitting president if there is significant support for the opposition in the primary. Don't know if this is correct but I don't really want to chance it with the crop of candidates the Democrats are currently fielding.

I know, we need to get away from political discussions I'll try to do better.