Curiously, the letter reads, "General election debates have a rich tradition in our American democracy, having played a vital role in every presidential election of the past 50 years dating to 1976." Although Lyndon Johnson refused to do it in 1964 and Richard Nixon declined in 1968 and 1972, the original TV debates were held in 1960 between Kennedy and Nixon.
Curiously, the letter reads, "General election debates have a rich tradition in our American democracy, having played a vital role in every presidential election of the past 50 years dating to 1976." Although Lyndon Johnson refused to do it in 1964 and Richard Nixon declined in 1968 and 1972, the original TV debates were held in 1960 between Kennedy and Nixon.
https://www.history.com/news/7-things-you-may-not-know-about-u-s-presidential-debates
They only sent the letter because they know Biden will refuse and that way they can look like a bastion of non partisan journalistic integrity.