I've worked with lots of PhDs. They're great for focused research into an unusual question, but often hopeless at dealing with practical problems where lots of fuzzy competing issues come into play. I've known a few who are good at the practical side (rlseiver, Rob Wolf) but many prefer messing about with an abstract model to actually coming up with a solution to the problem that might get implemented.
This is a natural consequence of the PhD process--it's disconnected from the needs of actual customers. Since grad students are the labor force for research professors they consider a finished dissertation equal to manumission and throw all the obstacles they can in front of it. This trains the candidates to concentrate on theoretical purity so there can't be any nitpicks from the review committee. This is the opposite of what's need to perform in a political job.
We've already tried having a president with a PhD--Woodrow Wilson. He created a theoretically perfect peace settlement for World War I . . . and gave us WWII. I'll take graduates of the school of hard knocks, thanks.