I agree, and of course, as an issue, it will work on some of them. Some of those irrationals are in the press, and tell us every chance they get that Trump is a racist bigot, see birtherism applied to Obama.
My point is that I don't think this issue will "turn the election," it won;t trun off enough of the black voters. The black voters that are turned off to Trump after birtherism, are the same ones that wouldn't vote for him no matter what. There might be some marginal changes, but you know, I think those could go either way. Irrationality is common, but not at epidemic levels!
FWIW, the press is telling us that birthersim hurts Trump with white educated females too. "It's not just a black issue" is something Lemon, Van Jones, and the white race hustlers are sure to add as they paint Trump as a racist bigot.
It occurs to me that Trump has given notice to the democrats and others who want to get mileage out of the birther issue, that this will not be a pursuit of his administration. He has said that Obama was born in America. That leaves the public to speculate on the various other legalities which might affect his status as a bonafide citizen of the US. The democrats would like to do what they are presently engaged in. Tie up the Trump administration with investigations into unsettled matters from a past administration. They want to impede the current one from taking on the business of cleaning up and moving forward. Chaos and disruption by whatever means is an ongoing tactic of the democrats. President Trump knows the game and deals with it.