We can debate the NATO 2% argument til the cows come home, but I believe the US position has merit.
I find it ironic that you cite 2nd world countries doing peacekeeping to earn hard cash, and then trash what is inevitably the paymaster for this, the U.S. Until such time as the 5 veto votes in the UN are rescinded (which will never happen), the altruistic vision upon which the UN was supposedly founded will never be realized; why would anyone with a shred of common sense look at the UN with anything but skepticism?
Reform at the UN is long overdue, if it takes a disruptive, reviled, ridiculed (by some) President to point that out, then collectively the organization, and its' leadership, has failed.