It's easy to forget that, before the 2010 amendments to the Federal Rules of Civil Procedure, attorney communications with testifying experts and drafts of expert reports were often discoverable by the other side.
The amended Federal Rules offer more protection to those kinds of materials. But since the change, some attorneys have become much more open in their communication with testifying experts, and some experts have become much less sensitive to avoiding written records.
But post-2010 Rule 26 does not protect everything relating to a testifying expert's work. In fact, it has gaping holes, and protects only two things: "drafts of any report or disclosure" and "communications between the party's attorney …