What does the rise of libertarianism portend for the future of the US? This is not a question of interest to Americans alone. It matters almost as much to the rest of the world. A part of the answer came with the publication of a fiscal plan, entitled “Path to Prosperity”, by Paul Ryan, Republican chairman of the house budget committee. The conclusion I draw is the opposite of its author’s: a higher tax burden is coming. But that leads to another conclusion: much conflict lies ahead, with huge implications for politics, federal finance and the US ability to play its historic role.

An analysis of the Ryan plan by the Congressional Budget Office makes the point (see charts). Its “extended-baseline scenario” assumes that current law remains unchanged. Under that assumption, revenue would rise from 15 per cent of gross domestic product to 21 per cent in 2022 and on to 26 per cent in 2050. Spending would rise substantially, too, from 23? per cent of GDP in 2010 to 30? per cent in 2050. As a result, the deficit would fall from today’s levels while debt held by the public would rise to 90 per cent of GDP in 2050.

As the CBO makes plain, this is an optimistic scenario. Current law includes, most notably, the assumption that the 2001 and 2003 tax cuts will expire, as legislated. Together with the impact of fiscal drag from economic growth and inflation, this generates the rising share of revenue in GDP. On the side of spending, the share of social security in GDP rises modestly, from 4? per cent of GDP in 2010 to 6 per cent in 2050. The share of all other spending (including defence), apart from that on health, is assumed to fall to close to its long-run average of 8 per cent of GDP. But health spending explodes, from 5? per cent of GDP in 2010 to 12? in 2050.