President Joe Biden tested positive for COVID on Saturday, his second positive test in two weeks. The president’s physician, Dr. Kevin O’Connor, said it was likely a “rebound” case, a phenomenon that has been seen in a small number of patients treated with Pfizer’s Paxlovid medication. “The President has experienced no reemergence of symptoms and continues to feel quite well,” O’Connor wrote in a memo. “This being the case, there is no reason to reinitiate treatment at this time, but we will obviously continue close observation.” Biden, 79, first tested positive July 21. After treatment with P…