Let's try again, because nobody has given an answer, so maybe you guys just don't know. It only requires a little knowledge of the electoral college system and 6th grade math. This time let's make it a multiple choice answer: a. 15% b. 25% c. 34% d. 50+%
If the suspense is killing you, here is an answer, although this result wasn't included in my choices, but I have to accept it as a theoretically correct one: http://www.squarefree.com/2004/11/01/winning-an-election-with-22-of-the-popular-vote/