There's nothing new or earth shattering about it. Presidents have assumed near dictatorial powers during national emergencies before. Lincoln during the Civil War and Roosevelt during WWII come to mind. After the emergency passes, things have always gone back to normal.
In the event of a national emergency, such as a nuclear attack, better to have one man or woman making the tough decisions, most of which would need to made at a moments notice. There wouldn't be time for long, drawn out "discussions" in Congress or a cabinet meeting or anything else. The man or woman making those decisions should be the President, IMO. If there were ever a time we needed to trust the person we put in power (and stay the heck out of their way), that would be it.