Does the US electorate agree with the birther stuff that Obama was not born here?
I for one symphatise with the birthers. Obama has not conclusively proved his birth and Sheriff Arpaio is doing an investigation.
Republicans should use the birther issue more. Why are they not pursuing it?
No they don't, because the issue has been sufficiently demonstrated in Obama's favor. The Republicans ignore the issue because it would make them look stupid, and the people stupid enough to believe it are going to vote Republican anyways.