HBC, the problem with a limited strike is that it wouldn’t stay limited.

The problem goes like this.
Topeka, DC and LA all vanish in a blinding light.
How? Long range missiles from russia or china? They will be seem and before they had landed, our response will have been sent.

Pakistan, Israel and others see this and its time to settle old scores.

Ok, suitcase bombs.
Right now that’s about the only way for anyone to remain even slightly anonymous. But then the CIA will be cut loose to do the voodoo they do. Granted they have issues in peacetime but when the reins are cut loose, it wouldn’t take long and reprisals would begin.

Hmm, high altitude EMP. (Satellite)
Considering we know about every piece of space junk up there and who put it there, something happens over Topeka we have a fair idea who did it.

That leaves rocket delivery.
From a cargo ship in the gulf, a suicide jetliner or such.
Its unlikely to take down the entire country, portions yes and unlikely the majority of the military.

All will make a mess of civilian life for a whole, but all are still unlikely.

As for invasion, from Mexico for example.
EMP goes off, Texans are without cold beer and AC for two days.
Its gonna be a slaughter.
And the Texans will not be the losers.