Having made the threat now Trump has to carry through with it, otherwise all future threats will be seen as hollow. He can’t retaliate against the UN - that’s just the venue. He has to retaliate against the individual countries. The question is how?
I suspect President Trump made the threat for the express purpose of cutting off their funding and saving American money. They played right into his hands.
He should retaliate against the UN, first step should be telling them their US headquarters status is void, leave by the end of next year. 70 years of nothing but subsidizing a bunch of low lifes who would be better suited to having the next HQ in Uganda or Yemen. They can raise the level of the economy of either place.
20% across the board reduction in US Aid should send a pretty clear message...
CUT off Foreign Aid to all these countries.
We can use the money here at home for our own uses.