It is merely a custom to make the transition smooth, because all claims for the office are terminated once the losing candidate concedes.

Pennsylvania, Georgia, and Nevada will recount the votes, and Arizona is still counting votes. According to Amendment 12 of the US Constitution, if the election cannot be settled in court, and it cannot be certified with an indisputable majority, the election becomes null and void, and matter goes to the the House of Representatives. At this point, the president will be elected by the House of Representatives. The Constitution stipulates that each state will have only one vote. Despite the House having 475 representatives, only 50 will be voting. 37 out of the 50 states in the House have a Republican majority, so the constitutional solution likely will lead to Trump holding office for a second term. -GEG