So, when does Wagner's Law kick in then?

Wagner’s Law is the idea that as a place becomes richer the inhabitants desire - and get - more government:

Wagner's law, known as the law of increasing state spending, is a principle named after the German economist Adolph Wagner (1835–1917).[1] He first observed it for his own country and then for other countries. The theory holds that for any country, that public expenditure rises constantly as income growth expands. The law predicts that the development of an industrial economy will be accompanied by an increased share of public expenditure in gross national product.

That is, that government is a luxury good. No, not a luxury, but something that we spend more of our incomes upon as our incomes rise. If you choose a wide enough band of incomes everything is an inferior, normal and superior - that latter being synonymous with luxury - good at some point in that distribution. We ourselves would hesitate to say that government itself is the thing desired but some things that governments oft provide certainly are luxury goods, public health to health care itself, social insurance, education systems and so on. Many of our own arguments revolve around whether it should be government trying to provide - badly and expensively as it does - those things we agree a richer populace wants more of.

But let us accept the argument, the Law, as it is. Richer places desire and get more government. Thus the inevitable rise of taxation and political direction of resources as the economy grows.

OK, now the economy is shrinking - has shrunk. Which means we need to slash government, doesn’t it? If GDP falls by 25% - not far off what is likely to happen in this short term - then that means we need, to accord with the law, to cut government by more than 25%. Not just to cut the cloth to suit our means, but because as poorer people we desire less of that luxury good, government.

Of course, we believe that swingeing axes and slashing swords should be applied to government and political budgets under near all circumstances but this law does move the idea from an expression of our preferences to a scientific truth. If it is true that government should naturally be a larger part of a richer economy then it must be equally true that it should be a smaller portion of a poorer one.