The reason it's a non-starter are manifold:
1) To defeat Obama this time, a LOT of people that voted for him last time will need to vote for the Republican candidate this time.
2) The overwhelming majority of these people are Democrats and Independents.
3) The ONLY people that the birth certificate issue has any traction with are people that didn't vote for Obama last time, hate him, and have no intention of voting for him next time.
4) Ergo, it would be stupid for a Republican campaigner to focus on an issue that ONLY appeals to people that are already going to vote Republican anyway.
To defeat Obama this time...
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You assume Obama will run. All it takes is 1 state to mandate that all candidates running for office must simply show proof of eligibilty (long form).
That right there will defeat the Kenyan.