Oh, it definitely is. If executive privilege doesn't cover conversations with a president's national security adviser then it covers no one. And, at a minimum, the Presiding Justice, and the majority of senators would acknowledge the right of either side to get a court ruling on that. But that works against the dem's goal of having the impeachment over by the end of October...which then became by the end of December.......which then became before the primaries........... .......... ....
Having said that, some dems like to point out that a couple Trump appointees have already testified regardless of the law and that Bolton might do that. To which, I say, fine. I am not convinced that he wants all his fox news and think tank commentator gigs around DC to come to a screeching halt by becoming the man who trashed Trump from the inside. So dems need to watch their arses. Bolton despises the dems despite his issues with Trump. We are not talking Romney or Jeff Flake or something like that here.
Again, no heartburn for me on the witness thing either way by anyone saying scary things. Some blood on the floor does not bother me, and was a foregone conclusion when an outsider busted his way into DC. Not the last impeachment scam to come either.
Crimes and are not covered by executive privilege.
When George Washington denied congress papers related to the Jay Treaty in the first use of executive privilege he stated that executive privilege covers all matters with the exception of impeachment.