can anyone explain why they did not act ?

it was extremely clear this was a foreign threat, is that not the purpose of having a nations military

there is a rumor they were blackmailed with threats against civilians, even the threat of a nuclear weapon used on US civilians (!?)

"Time is the sovereign remedy for the effects of calumny, as for the other ills of life. Should the world condemn any particular line of conduct on the part of any man, if that man wants a quiet life, his best course is to stick to that line of conduct.

After a short time the subject will become stale, and the railers will drop it, were it only in order to look out for some fresher subject for their railing. And the more firmly and consistently we pursue our way, disdaining the idle censures of society, the sooner will men come to accept as reasonable that which at first they condemned as the reverse.

For the world seldom imagines that the man who steadily persists in any given course may be wrong; and ends by condemning itself, and acquitting him. Hence arises the well-known fact that weak men are governed by the will of the world, but strong ones by their own." - Giacomo Leopardi 1820