(zik, zik, zik...sharpening Occam's Razor on a leather strop while posting)
If there were such an event actually in the offing, there wouldn't be a doggone thing that the full, combined resources of the world could do about it, let alone some poor fighter jock in an F-18. Or a whole bunch of them. Or all of them, all together.
The physics involved in stopping or deflecting say, a million ton piece of iron and nickel moving at the modest interplanetary relative speed of 20 kilometers a second are simply staggering. Even if there were plenty of notice, what're we going to do? Pop a bunch of nukes off in space in front of it? We end up with, at best, several pieces or a lot of pieces of iron and nickel, pretty much the same trajectory, and pretty much the same mass at about the same speed, only now it's a shotgun blast instead of a rifle bullet.
Our intrepid and heroic F-18 Squadron Commander with the granite jaw and the sexy 'Iceman' nickname at Angels Twelve over the Indian Ocean somewhere sees a brilliant flash of light for an instant, just before his plane comes apart around him from the shock wave.
No, either it really is some kind of huge 'surge exercise', or there's something dark going on in the military and diplomatic world. Maybe we're sending the PRC a message in response to something that they're poised to do, or something.
Well, we could draft an eclectic team of oil well workers to fly to the asteroid, drill an 800 foot hole, insert several nukes, and blow the thing up.
I'm sure the gov't has "gamed" such a scenario.