It’s been a frequent topic in our house, with one party agreeing with you, and me believing that there are in fact people who would care. Certainly not his diehard supporters, but on the fence types who would not like the idea of a man who was an illegitimate child as president.
Probably affected by voter age.
He was quite obviously conceived out of wedlock, but the legal definition requires birth in marriage, not conception. A child born 10 minutes after the ceremony is just as legitimate under the law as one born 10 years later.