That throws the big one...

Tactical Nukes are already in place... Tactical... I mean ones fired out of Artillery... small payload... but still very devistating but on a far smaller scale... I believe[1] the largest ones are around 500 Ton Yield... but those are usually used in Naval Artillery(really big bore ones at that) *IF* they ever get taken out of where they are stored on US Shores (maybe there are already). The ones I believe they have right now are about 125 Ton Yield[2].

So, I don't believe you'll see the *BIG* one get dropped... or sent over in a Missile... Just a few discretely[3] used Tacticals should appear...
[1] Heard from a few different Naval Artillery people I know... but that is their Guestimate.
[2] Once again, a Guestimate taken from different articles discussing them over the years.
[3] By discrete, I mean that *sarcastically*. Ain't no-such-thing as a Discrete Nuclear Explosion.