What common sense? What common sense informs you that obstruction must be successful in order to be prosecutable? Does a person not get charged with attempted murder if they fail to kill their intended target? This is no different in that sense; Trump can be charged with an attempt to obstruct justice if Mueller presents such a case to the Department of Justice.Where in the law prohibiting obstruction of justice does it state the obstruction had to be successful in order to be prosecutable??Even worse than that, Trump tried to silence Comey with the threat there could have been tapes.I don't think Comey gives damn .. he didn't lie.
Obstruction.
He didn't silence Comey and your dreams of impeachment are, "what, are you crazy?", why torture yourself..
I'm not a lawyer, I'm just blessed with common sense..... well, mostly..
keep your dream ...