The real investigation (Mueller's - forget about Little Devin's clown show) has been going for only ten months. You have no clue what evidence there is, but obstruction of justice is one that it would take a complete idiot not to see.
The investigation has been going on for over two years, first under Comey and McCabe and then under Mueller and so far we have not seen a single piece of evidence of any collusion between the Trump campaign and the Russian government. The only reason for a special counsel was the false allegation of collusion between the Trump campaign and the Russian government meant a possible conflict of interests existed, but now that we know there never was any collusion - which would not have been a crime, anyway - there is no reason for a special counsel.
Only an idiot would be claiming there are grounds for obstruction of justice in firing Comey or there would be such grounds if Trump fired Mueller. An intelligent person, would recognize that if evidence of collusion had been found, while it would have been politically damaging to Trump, it would not have been a crime, so Comey had no business investigating it unless it was for purely political purposes, which would be a crime, and an intelligent person would recognize that there are no solutions to the conflicts in Syria or in eastern Europe without good faith negotiations between the US and Russia and this phoney investigation into unfounded collusion investigations make such negotiations politically impossible, and would conclude however obsessed you are with getting Trump at any price, firing Comey corrected the injustice of the FBI investigating actions that were not crimes and firing Mueller, if he does, would simply be returning the investigation to the Justice Department where it belongs.