Let me make this as clear as I can. If Trump had walked up to Comey and said "I order you to drop the matter and will fire you if you don't" that still would have been legal. As the president, that's completely within his power and is not obstruction of justice. We don't have to dance around whether it was an implied order or threat or whatever.
You are right that the President has exactly that right and we would still be in the same place we are at right now. Comey could refuse, tell the AG. Trump could threaten the AG and fire him and Comey if they do not comply. Then Congress would get into the mix because then it becomes the same incident it is today. The fact of the matter is, obstruction of justice is when the president steps in the way of an active investigation that ties him or he is involved. Its why people in government like Sessions recuse themselves from such things because of their interest and its the reason the President should do the same. If not then he forces Congress to step in and find him obstructing justice which is a impeachable offense. Saying that Trump has the right to do something and forgetting that not all actions do not lead to him getting canned is ignoring how the US system works.
We are here today because Trump in his infinite wisdom decided to go on national TV and admit that he fired Comey over an investigation that involved him. He had the excuse from Session and Rosenstien but instead he wanted it to be about his decision and about himself. Because of that ego, he place himself in legal jeopardy and reaping all the rewards. Stop defending this guy for people an idiot and not following direction when people actually give him his outs.
Even the payment hush money is another prime example. If you have all that crap stored in your locker and you know paying someone to keep quite while you are on the campaign trail doing your thing, it probably would have been best if he just admitted he had some questionable relationships got in front of the whole thing and moved on. Liars never do stuff like that and people like Trump always feel they can slide by any law or not get caught. If he gets impeach its because of his decisions and his alone. People need to stop trying to be his savior.