I'm not a big fan of the doctrine of executive privilege which contends that a president can withhold information resulting from the internal operation of the executive branch of government. Its invocation, as Richard Nixon's effort to suppress the release of the Watergate tapes illustrates, is used more often than not to keep information critical to the functioning of our democracy from seeing the light of day.
That said, it makes sense to me that presidents should be able to engage in frank, off-the-record, private conversations with individuals, including other world leaders. I believe this because such conversations are an important way for them to explore the range of policy options, some speculative, that are part of good decision-making. Releasing a transcript or compelling testimony by third-parties would have a chilling effect on such discussions.
Of course, this note has to do with the recent demand that the interpreter present at the private conversation between Donald Trump and Vladimir Putin in Helsinki Monday be subpoenaed by Congress to testify about what she heard. Although a congressional committee could issue such a subpoena, it's hard for me to imagine that it would be upheld by by a federal judge when confronted with assertion of executive privilege for the reasons outlined above.
Might there be exceptions? Didn't Nixon end up having to release his tapes under threat of a subpoena after all?
I do think that there are exceptions and that they mostly have to do with demonstration of probable cause that conversation in question was implicated in the commission of a crime. In spite of the clamor about Trump being a traitor, I suspect that the standard of probable cause would be hard to meet in this instance. My guess is that most federal judges - and ultimately the Supreme Court - would see this subpoena as little more than a politically motivated fishing expedition.
And, in the usual and understandable rush to undercut Donald Trump, we should consider what would be lost if such a subpoena succeeded. Well for starters, as an article in the New York Times today points out (see "Who Heard What Trump Said to Putin? Only One Other American" in the comments), it would compromise the professional ethics of people who serve as interpreters. The likely result being that only political lackeys would be selected do a job that demands the highest level of language expertise.
More significantly, and something that appears to be lost on Trump opponents who are forever looking for new legal mechanisms to thwart his administration, it opens the door to all conversations between future presidents and world leaders where an interpreter or a notetaker is present being subject to revelation by subpoena.
For example, would we want President Elizabeth Warren's private discussions with her Chinese counterpart to always be a matter of public record? Do we really want already trigger-happy Republican congressional committee chairs - I'm looking at you Trey Gowdy - turning every trip by a Democratic president abroad into a subpoena battle?
Finally, although there's absolutely no changing their minds, Republicans are using what they see as politically motivated legal tactics to convince their base that legitimate legal process, like the Mueller investigation, are nothing more than cynical sour grapes on the part of Democratic losers. Calling for the subpoena of Trump's interpreter in Helsinki plays right into their hands.