This wasn’t an investigative probe into Donald J. Trump’s tax returns or charitable donations. Then again, the Trump family dynamic is almost as mysterious: His children’s obedience, loyalty and nearly impeccable public demeanor impresses even some of his harshest critics. A lot of voters say they figure he can’t be too bad if none of his children has defied or disappointed him. (Quite the opposite: They are so attentive and doting I called them “helicopter offspring.”)

Tiffany, 22, seemed to be in the same mold, but nobody knew much about her, and many were curious about whether and how she measured up against the three adult children from his first marriage.

I hadn’t expected this kind of resistance from the campaign when I started the reporting this summer. I began the usual way: searching news clips, Facebook, Twitter and LinkedIn for people who knew her in high school and college, in Los Angeles and New York, and asking Trump family friends all over for their insights. Some said they had nondisclosure agreements; others said they had to get permission from the campaign before talking.