Okay, correction on my part: It wasn't Brennam who admitted drone strikes were unconstitutional. It was Holder (the Justice Department guy... you know, the lawyers everyone cites here).
http://www.mediaite.com/tv/ted-cruz-goa … itutional/
Yes, the answer came after 5 minutes of pulling teeth. I'm not saying the answer was easy. But there's actually an answer, sworn on the record, from the guy running the department who gives the legal advice to the Obama Administration.
Remember, Holder and everyone else in the debate is making a distinction here between imminent threats (the guy aiming a bazooka at the White House) and people sitting in coffee shops. The link you cited, Kemp, clearly states that Holder believes in the imminent threat scenario, drone strikes would be legitimate. Nobody's challenging that. On the other extreme, there's clearly a quote (albeit after some teeth-pulling) that has the Justice Department under oath stating a legal opinion on the subject. (Yes, they're under oath when they testify before Congress).
So no, I don't think this is a question of the Obama Administration wanting the right to bomb shoplifters at grocery stores. Rather, I would say it's simply a matter of administrative inertia. Making a judgment call on the constitutionality of anything is an enormous responsibility, one way or another. Make too broad a Constitutionality judgment too soon, and you could create a seriously screwed up precedent in the future.
Does this mean I disagree with Paul? Absolutely not. The filibuster was a good method to shake things up and try to goad the Administration to engage in the debate. That's what a filibuster is: a way for a minority to shake things up and get some awareness of an issue out there. But agreeing with Paul doesn't mean you have to assume that the problem was a government trying to get the right to bomb Starbucks... particularly when Paul doesn't even take that stance (though he certainly could have if he thought it was an honest evaluation of the situation).