Trump realizes that his base doesn't care what Comey says.  These are the same people who voted for a man who was caught on tape boasting about sexually assaulting women.  Comey will testify, telling us what we already know.  Trump will then call Comey a liar and send out an apoplectic tweet storm, and his base will hoot and holler like a pack of jackals.

It's all so predictable that that story can be written long before Thursday.