I do not believe he will be removed from office...not a chance. But one impeacheable offense I can think of off the top of my head is using drones to kill American Citizens without a trial. He has done it at least twice.
i understand your sentiment, and i dont necessarily disagree (not sure i agree either) but thats a legal issue that hasn't been fully decided on in the courts
we're at war and the rules are different.....i have mixed feelings on the issue and honestly, i'd be a hypocrite if i wanted to impeach him for killing a treasonous American citizen taking up arms against our country