Graham would have to charge Schiff with treason, felony, or breach of the peace in order to negate Schiff’s immunity from being questioned”
While you may be right about Shifty Schiff, if Schiff met with the "whistle blower" outside of official Senate Chambers he could be called as a fact witness. Also, the speech and debate clause does not protect Shifty Schiff’s staff who are up to their eyeballs in this con.
They can question Schiff about contacts on his own time outside of chambers, or call his staff instead of him.
-PJ