I don't care if Obama was born on the moon. His mother was a citizen at the time of his birth, so he is, too, even if those very official-looking documents were a clever forgery. Even if he wasn't, it doesn't really matter as much as his policies and actions. The whole birther argument is a diversion (even by political media standards, where most stories are diversions and sensationalism), for both Obama and Cruz.
Trump has absolutely zero chance. He's doing well in some polls, yes, but he's hit his ceiling. The majority of people, even in the Republican party, wouldn't vote for him. It's just disaffected people who want a non-politician and hate Mexicans. Also, he's not socially conservative, so the anti-establishment voters who want a socially conservative candidate will go to someone like Cruz after the Donald's announcement bump fizzles out.
But I agree it would be very fun to see him in the debates.
Trump needs to somehow be trumped. He could singlehandedly give Hillary Clinton the keys to the White House if he doesn't shut up. The Republicans don't need any help at sabotaging their own campaigns. That, and there's talk of him considering running as an Indy in the general if he doesn't win the GOP nomination.
If he runs as an independent, I agree, that would be a big help for Hillary. But I don't see how his primary run makes the Republicans look bad. If they consistently oppose his more extreme views, he'll actually make them look saner and more mainstream to moderate independent swing-voters.
Donald Trump's out calling Mexican's "rapists." Ted Cruz doesn't look as crazy as he did to some before.
I love how Trump is running. He's always good for some headlines and narrative that no other candidate would produce.