Even if Obama were an open book, with stellar transcripts, and was wildly successful before becoming president, none of that matters in comparison to his reign as POTUS. As president he has failed utterly to make this country, it's people, and our place in the world, better than before he became president.
In fact, he's managed to make everything worse. Everything, if you can imagine that. Even his accomplishments that people can point to as good, all of them, every one of them, come with negative consequences, almost all them unintended consequences, which is the hallmark of bad decision making.