Interesting article. I didn't realize Buchanan ran against Bush in 1992. Seem like a bit of a self fulfilling prophecy - i.e. you probably have to be a flawed President to be vulnerable to a serious primary challenge, which would then lead to you losing the general election.
I kind of think the only realistic way Trump wins reelection is if the left ends up with some batshit crazy candidate that is anathema to moderates.