It wasn’t the next day. He tested positive, went to Walter Reed on October 2nd, returned to the WH on October 5th. On the 7th, his doctor said he’d been symptom free for 24 hours. On the 12th, his doctor said he’d tested negative 2 consecutive days in a row. https://www.politico.com/amp/news/2020/10/12/trump-negative-covid-not-infectious-429068