2) The world economy is unbelievably strong. World consumers may very well be keeping the US economy afloat, through US exports.
I don’t see a slump in US consumption (which would be mitigated by rising US incomes,) causing a global downturn. Now maybe global growth rates might slow, although I have no idea how to quantify the reduction. But a downturn? It seems we are a very great ways from that possibility.
I admit I may be associating too much with the term “downturn”. If by “downturn” you mean “undetermined reduction in growth”, then I retract the previous objection. But if you mean “recession” or the like, then I cannot agree, at least at this time.