So let's follow your developing reasoning here a while:
So you got 20 suitcase nukes in country. Not 10, not 30. The number is 20. That's what you've got to 'finish off' the US. If you're a 'strategicly' (that's not English either) minded organization I would suppose that first you might want to decide what the term 'finishing off' means.
Unable to respond? Unable to function as an integrated society? Ready to surrender and put our heads on the chopping block?
If you mean 'unable to respond'? That means hardened targets; not a Queda MO. 'Unable to function'? 20 small nukes aren't gonna do it, unless you know of 20 absolutely critical spots in the country that, if destroyed, would mean the cessation of all activity.
That leaves 'ready to surrender'and I don't know about you, but I'll be at the barricades waiting for the big follow-up invasion.
Any other ideas?
PS: I'm aware of the al Queda operational philosophy so you can stop with the lecture.
Look what three airplanes crashing into buildings did to this country! The overreaction would be hyperactive, profound, and permanent. It would be even more senseless than the mindless overreactions to the 911 attack.