Forget asteroids as weapons.
Can't think of O.B.L. getting hold of one,
nor can Saddam Insane.

But what if?...What if [hypothetically]
a huge Asian nation, already possessing
nuclear & space-access technology,
were to send a 400KT nuke device,
with its own hypergolic propulsion
system & guidance and command-control
hardware/software, to the moon, and park it in Lunar orbit?

What if it stays in Lunar orbit under the
'official' pretense that it's a science mission?
Even the CIA swallows that line.

Months later, the media has forgotten
about it, but tensions are building between the USA and that huge Asian
nation [perhaps over Taiwan].
That huge Asian nation sends an encrypted command to its lunar-orbiting hardware: The coded message
to that lunar-orbiting craft commands
it to divide [leaving one part in Lunar
orbit with a transmitter, and the other
part (the stealthy-nuke and it's propulsion system) to head back to Earth]
A few days later, that stealthy 400KT device, encased in ablative heat-shield and radar-signal-absorbing material
silently plunges into Earth's atmosphere
above the states of Virginia and Maryland.
NORAD's radar systems didn't pick it
up until the object's atmospheric entry....Too late.
The 400KT nuclear blast, high over
D.C., generates a huge EM pulse that
cripples electronics throughout the D.C.
area.
Suspicions fall on that huge Asian
nation. Predictably that nation denies
any involvement.
The crisis leads to the U.S government
breaking off diplomatic relations with
that huge Asian nation, and not much else; Some sanctions, a show of the
US fleet, and the Security Council voting
to condemn that nation. But no retaliatory nuke response.
Those in that Asian government laugh their heads off at the impotent response.

Jacob