How can a fictional cartoon character be president? I even once read in an old issue of Nintendo Power that Mario was running for president and had promised everyone "Pasta in every pot, and a Nintendo in every house."
You'd think Sonic would be his rival, and then there would be really ugly attack ads on both sides that would make Bowser and Eggman blush with shame, and instead of mudslinging Sonic and Mario would be flinging fireballs and chili dogs at each other. That would actually be pretty interesting.
And then there would be all kinds of sleazy gossip about First Lady Peach or Amy Rose or whatever. The tabloids would be screaming everywhere you looked.