Why is he not immune? He has a Constitutional immunity, which is Supreme Law of the Land.
The "whistleblower case" stems from whistleblower legislation passed by Congress, supported by the Intelligence Inspector General statutes, also passed by Congress. Both of these are inferior to the Constitutional privileges and immunities clause.
The Senate can make the case that Schiff committed a felony in his interference with the whistleblower or the IG, but that's more than just calling him to testify as a "fact witness." They'd be calling him to explain a felonious act, which would instantly inflame Pelosi and Schumer.
The only recourse for a person who abuses his authority is expulsion by 2/3rds of the chamber, or a devastating PR campaign in his district to compel his constituents to not reelect him.
-PJ
Hey PJT, Schiff’s immunity is limited to his acts on the floor of Congress, not to actions as his staff did by coordinating with Eric CIAramella prior to his filing with the new “hearsay” rules to the IG Deep State clown.
So IMHO, this is no hollow threat. Schiff can very well be called along with CIAramella to explain what they did together.