If you play threat from the east and choose discard 3 then draw 3 and you can't discard any cards, can you draw 3 cards? If you choose draw three cards then discard three and you can't draw, do you have to discard?

Whenever an effect says to "then" do something, the part before the "then" must be completely successful before the part after the "then" can happen at all.

So in Threat from the East, if any player is unable to draw or discard all three cards (whichever you decided to do first), no player will get to do whatever would come second (although everyone must do as much of what you choose to do first as they can).

Thanks ktom. You always give good, reliable answers.