If that's so - and it may well be - then it is different in kind from this matter, where "safety" and liberty are, and have been, in conflict. The job of the POTUS has little do with safety, but much to do with liberty.

The POTUS is using this "my job is to keep Americans safe" line to make a very tenuous tie to a position he wants to take on solitary confinement.

Using your analogy, imagine the bus driver said "It's my job to keep the kids safe, therefore I'm going to start requiring all the kids to give me their cell phone numbers in case there's an emergency."

Could that be construed as "keeping the kids safe"? Sure, but that wouldn't necessarily make you any more comfortable with the bus driver gaining more intimate access to your children.

I know analogies are never perfect, but another nitpick with this one is that the POTUS holds a position of power and authority that you wouldn't typically have to worry about in your average bus driver, so additional scrutiny into "Just what did he mean by that?" is occasionally warranted.

Justifying the move as a step to keep America safe is the right move in this political context. America is generally fearful right now, so Obama's political adversaries will attack this move as eroding the safety the prison system attempts to maintain.

"My job is to keep Americans safe" is an acceptable justification for limiting solitary confinement. It would not be an acceptable justification for extrajudicial killings.