The letter writers, noted that Netanyahu is a weak leader, blinded by political power. He is , too reliant on the religious right, the extreme Zionists ( Bennett) and the settlers/occupiers. He has shown that he will use the "security card" ( which the letter-writers state is no longer real), to rally support and has shown time and again that he is not interested in resuming the peace talks with his continuous sabotaging of it with more settlement building in East Jerusalerm and the West Bank.
The Americans are also becoming tired of this also as demonstrated in a recent interview by a high administration official, calling Netanyahu, among other things a "chicken-shit, and the the snubbing of the Israeli Defense minister on a recent visit to Washington.