It depends on how you're defining the word "god":
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god
noun \ˈgäd also ˈgȯd\
1. God : the perfect and all-powerful spirit or being that is worshipped especially by Christians, Jews, and Muslims as the one who created and rules the universe
2. : a spirit or being that has great power, strength, knowledge, etc., and that can affect nature and the lives of people : one of various spirits or beings worshipped in some religions
3. : a person and especially a man who is greatly loved or admired
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If you're using definition #3, then yes I do believe in the existence of george w. bush and barrack h. obama.