Well, yes, the birthrates and immigration can help the U.S. but that was not the point the OP was making -- and I am making too -- Japan has showcased boundarie

Well, yes, the birthrates and immigration can help the U.S. but that was not the point the OP was making -- and I am making too -- Japan has showcased boundaries one can reach on relation to debt and fiscal policy; and also that negative interest rates and meddling with rates does not work per se and out of the box.