He may not feel he needs 45s testimony for an obstruction charge.

Enjoy what?

For starter's, their ruthless, baseless pursuit of Bill Clinton come back to bite them on the a$$.

Sid

the Subpoena of the Nixon tapes are precedent but he never sat before a grand jury-so this might be a matter of first impression

Note in Jones v Clinton the SCOTUS ruled 9-0 that there is no immunity from proceeding with a civil case while a President is sitting in office but held:

The court also found that "our decision rejecting the immunity claim and allowing the case to proceed does not require us to confront the question whether a court may compel the attendance of the President at any specific time or place."[1]

https://en.m.wikipedia.org/wiki/Clinton_v._Jones

Doesn't seem very voluntary to me.

....and the SCOTUS expressly said it was an issue they weren't ruling on. Significantly it would probably take at a minimum of 6-9 months to get a final ruling even if the issue was expedited through Trial Court, Appellate Court and SCOTUS so you better be prepared that Trump can extend determination of this issue by playing hard-ball

the most likely outcome is that it would be defeated either in the House or the Senate.

Next January, assuming the D's control the House, we will be in a much stronger position.