The expression 'not that bad of a'
Solution 1:
Of as a preposition is also:
- used to indicate an appositive: that idiot of a driver.
appositive:
- A noun, noun phrase, or series of nouns placed next to another word or phrase to identify or rename it.
http://www.googlefight.com/index.php?lang=en_GB&word1=Is+Obama+that+bad+of+a+President&word2=Am+I+that+bad+of+a+person