That issue was raised because it hadn’t been hashed out yet and was ripe to use as ammunition, especially since it is relevant to Trump’s touting of his business success.
No one has mentioned or cared about birtherism for years. Obama isn’t on the ballot. Trump injected an issue that hurts him into the debate, and far from “getting out ahead of it”, he lied as to how it all went down, and the most cursory search on Google proved him a liar. A foolish, unforced error.
You’re really quite clueless as to American politics, aren’t you?