"misunderestimated"

«They misunderestimated me.»

- George W Bush , Bentonville, Ark., 
(Nov. 6, 2000)









Misunderestimated? I was trying to understand this vague sentence and wondering what does it means. The Mr. President was trying to say they "misunderstand" or "underestimated" him? Or may be BOTH? 
Well, George W. Bush is well known for his occasionally unconventional use of English! 
At least, Wikipedia is right about "Bushism". :)