Comey did NOT exonerate Trump.
He said hew was not personally under investigation AT THE TIME.
Trump wanted Comey to say that publicly.
Comey refused because Trump might come under investigation in future.

Trump asked Comey for loyalty, 
Trump asked  Comey to let Flynn go.
Comey fired Trump because of "the Russia thing."

But you don't see anything worth investigating. LOL!

It's not just the Democrats who are investigating. Bi-partisan committees in the House and Senate are investigating. 
Trump's OWN Justice Department is investigating and hired a special prosecutor!