Because he are smart.
"People say, how can I help on this war against terror? How can I fight evil? You can do so by mentoring a child; by going into a shut-in's house and say I love you."
"There's an old saying in Tennessee-I know it's in Texas, probably in Tennessee-that says, fool me once, shame on-shame on you. Fool me-you can't get fooled again."
"This foreign policy stuff is a little frustrating."
"For a century and a half now, America and Japan have formed one of the great and enduring alliances of modern times." ( well, except for that little war thing )
"I really, really like being the president."
And the ultimate reason is:
<font size="6">"I know the human being and fish can coexist peacefully." </font>
