NORAD is mostly a surveillance and warning outfit. They have interceptors, but not at enough locations, most of the time. Since 9-11 they've increased the number of birds sitting strip alert, which should be a big help. They also have decent ground based radar net, at least along the periphery of the country, which is shared with the FAA. That I know quite a bit about, since I just got off of a project using the real time data "take" from some of those radars for a training system.
Not only are their no strategic SAMS, there are no tactical ones "stood up" over the vast majority of the country, just a few mobile launchers protecting even fewer high value targets. I don't know if those are still deployed, but they were quite visible after 9-11. We are deploying the anti missile system, but that will be pretty thin and not good for much of anything but a rogue single or small numbers launch...better than nothing with nut cases like the Mullahs and Comrade Kim getting nukes and missiles. But until that begins to be deployed, NORAD is mostly good for telling you to put your head between your legs and kiss your... well you know... goodbye, as far as an attack that could be launched by Russia or China (or France for that matter!). Oh and of course the minor (NOT!) matter of telling the President when to retaliate and who against.
Most people are shocked to find that we never had an anti missile defense throughout the entire cold war period, when the Soviets had thousands of missiles pointed our way. We did have a few interceptor missles for a short time, but nobody had a lot of faith in those, although I think they would have done just fine, being armed with small nuke warheads, which would have exploded high up and well away from populated areas. (Even they probably would have been useless against an SLBM attack launched from a few hundred miles offshore, simply because the system could not respond fast enough to get them before they got too close or even to their targets.
Yes, and it's our air defense system. It's heavy on sensors and command/control, and the weapons are generally the aircraft.
Which brings me back to the original point - we have an air defense system.