Some of the documents appear to be detailed Ukraine battlefield assessments prepared over the winter for senior Pentagon leaders. But officials only became aware that the documents were sitting on a public server around the time that the New York Times first reported the leak, on Thursday, according to people familiar with the matter, who spoke on the condition of anonymity to describe an unfolding investigation. Senior Pentagon leadership restricted the flow of intelligence Friday in response to the revelations, two US officials said. One described the clampdown as unusually strict and said it revealed a high level of panic…