In short, he's not going to win the Republican nomination. He's not a threat.
And if he's not a threat, perhaps he can do some good -- as an attack dog. A good chunk of the population still clings bitterly to a personal admiration for Obama, even if many have soured on his policies and governance. What Trump brings to the table is a shameless, vulgar willingness and ability to attack Obama personally. What we know from three years of Obama media coverage is that anybody who criticizes Obama on anything other than the narrowest of policy grounds gets denounced as a racist. (Actually, any criticism of Obama is declared racist, but the policy stuff is less so.) Trump has shown an enthusiasm for criticizing Obama without any concern for how it might backfire onto Trump.
Yeah, the birther stuff was idiotic. But it must be noted that the mainstream candidates all distanced themselves from the issue, and thus won't be burned by it.
I'm a little more interested in the academic records. I'd like to know what sort of GPA our sooper-geenyus President was pulling at Oxy and Columbia. (I'm guessing it was pretty good, but short of great. Remember, Dubya the dunce had a slightly higher GPA than Kerry.) I'd love to know what courses Obama took. I'd consider sacrificing a pinkie toe to get a hold of some of his papers. Again, none of the mainstream candidates need bother with this down-in-the mud stuff. Trump can be the honey badger invading the beehive, unfazed by multiple stings from an angry swarm of media-types.
It's not that I oppose Obama because I think he might have had a less than stellar GPA, took a dozen courses on Marxism, or got a C-minus in basic economics. It's that I think finding out such information might start to dispel the rainbow-farting-unicorn aura that surrounds the man. People need to like Obama less on a "personal" level.
So I've made my peace with the Trump quasi-candidacy. Let him stir up the pot of Obama's history, then fade into political (if not media) obscurity after a while. He really can't hurt anything.