WASHINGTON — President Biden made a surprise nighttime visit to the Delaware home of Hallie Biden on Sunday — just before she’s due to serve as one of the most important witnesses at first son Hunter Biden’s federal trial for alleged gun crimes. Biden stopped by Hallie’s home around 8 p.m. for a brief private talk eight days before the 54-year-old first son’s trial is scheduled to stand trial beginning June 3. Hallie dated Hunter at the time of his alleged gun crimes and is one of a dozen expected witnesses.