https://edition.cnn.com/2020/11/07/opinions/trump-concession-norms-zelizer/index.html
If Donald Trump refuses to give a concession speech, it will be one of the last norms that he breaks as President. Now that President-elect Joe Biden has won the 2020 election, Trump will need to decide what to do next.
The good thing is that it doesn't ultimately matter. A formal concession after an election is not embedded in our Constitution -- it is a norm. Historians tend to date the first public concession back to 1896, when Democrat William Jennings Bryan sent Republican William McKinley a telegram that said: "I hasten to extend my congratulations. We have submitted the issue to the American people and their will is law."