A combination of millions of people with production skills in California, and a huge domestic market able to spend billions has fuelled one of America's biggest exports - TV & Movies. They're not the biggest exports in dollar amounts, petroleum brings in almost 50 times more, but they give America something else apart from money - soft power via an outsized place in global cultural consciousness.

What happens when that sharply recedes? Soft power isn't as easily counted as the size of aircraft carriers or the number of missiles, but its effects are real.