Rush, like most sane people, knows the question is meaningless. Obama will NEVER admit it, and what other proof do you have? Not much. The places that you may dig up proof is not talking.
Ok, so now you have a small amount of proof and take it to the SCOTUS. It is going to have to be OVERWHELMING proof from them to decide.
Now, the congress must toss the guy out.
We are talking years in a process that is meaningless and therefore lacks the need for ANY attention.
You also have the basic problem that destroys just about every government-related conspiracy theory: how does one keep such a huge secret in an open society?
Obama has plenty of enemies on both sides of the aisle who would love to discredit him. So first thing he had to do was neutralize the most ambitious couple on earth, the Clintons, and everyone who supported them. If you think about how the Clintons reacted to adversity (by digging up and releasing dirt on anyone who opposed them) it's amazing that Obama could derail Hillary's Presidential ambitions if he had that kind of a lie hanging over him.
Once he got past the Clintons he has to be able to control everyone else who oppose him, from Republicans to Independents to other Democrats, unless you are willing to believe he has 100% support from his own party. And not just high level leaders, he has to control everyone who works or ever did work at the Hawaii Department of Records, any school he ever went to and any other place around the world that would have some sort of traceability to his past. Even his inner circle can't be considered 100% reliable. The Nixon administration wasn't brought down by Congressional hearings or CBS news, it was brought down by a guy who was angry about being passed over for a job promotion.
Once he has all of these things under his control he has to keep them under control year after year through good news and bad, changing election results, hostile opponents, the media, young guns looking to make a rep for themselves. It's basically impossible to hold up as long as he has.
Rush realizes this so he keeps his distance and I don't blame him a bit.