For 1, just by talking with the press about the video he has authenticated it. It's an ironic move by someone who has kept his tax returns a secret despite the press hounding him over it because it would make him look bad. You would think he would have consistency in that regard.
And then there's what he did say when he decided to legitimize it:
Probably the worst offense comes right away: "I don't remember the question that was asked." is not a nice thing to say because it alienates the person/people who asked the question. Can you imagine if you asked the president a question and then he goes: "Well I don't remember who are what the question was."? It shows someone who doesn't see people, someone who's more impulsive then genuinely caring, even to the people who are his allies.
The "I also have a lot of people who will vote for me no matter what... at least I hope so..." does not ensure confidence in your faith that there are people loyal to you. How are the people going to feel they should vote for you if you're not sure there are people going to vote for you? It shows a bit of lack of faith in oneself that isn't attractive to voters.
And by the way, the whole "no matter what" thing is a bit of a stretch. If Obama suddenly sent in the army to detain as many Americans as he could and detained them via the NDAA of 2012 (going back on his signing statement) I'm sure that "no matter what" would be quickly disproven.