“Underlying each of the disagreements in the letter is not just a matter of historical fact but a conflict about whether Americans, from the Founders to the present day, are committed to the ideals they claim to revere. … Americans need to believe that, as Martin Luther King Jr. said, the arc of history bends toward justice. And they are rarely kind to those who question whether it does.” Adam Serwer looks into the reasons historians felt strongly enough to write the letter and the reasons that a number of historians asked to sign it declined, as well as which criticisms the project’s leader accepts. – The Atlantic