A FReeper posed an idea (maybe on Monday?) that Comey deferred to the DOJ to deny the wire-tapping allegations by Trump, because he KNEW the DOJ could not and so would not issue a denial, which in the end, helps Trump.
Just some food for thought.
The fact that Trump hasn't done so with Comey leads me to believe he has a reason for keeping him. I trust Trump on this and will let events play out.