The most crucial question about George Osborne's Autumn Statement is one he can't answer. Which way will the US turn over the fiscal cliff? By contrast, what the US does to its budget matters very much, and once the hubbub here dies away, the focus will I think shift to the US where the "fiscal cliff" looms. So let's for the moment think about the rather larger stage over there. The cliff is the automatic tightening of fiscal policy that happens, in the absence of Congress passing legislation to stop it, at the end of the year. The cuts in spending and the increases in taxation are equivalent to 4 to 5 per cent of GDP. It would be almost as though we here were doing our five-year squeeze in one fell swoop. But were it to happen, the shock would I think lead to some accommodation in Congress in January that would soften the blow. Both sides accept that there has to be some sort of deal, one that would trade higher taxes (which the Democrats stress the need for) with lower public spending (which the Republicans want). The question is over the balance. The more likely outcome is that there will be some sort of temporary deal in the next couple of weeks. This would pave the way for a more substantive agreement in the spring, which would be a sensible way to do it. The problem with the US tax system is that it does not raise very much revenue as a proportion of GDP compared with most Western democracies, but it has quite serious distorting effects on people's behaviour. It is too complicated, and combines quite high nominal rates of taxation with too many loopholes. Take even the basic income tax rate. The top take notionally is 35 per cent, which may not sound that high to us. But you have to add state income tax, the top rate of which could be as high as 9 per cent. So, rich Americans face nominal rates similar to those of Europeans - they just have more loopholes. There are two questions, then. One will be whether the deal will show a credible path towards a balanced budget. In other words, at what speed will the US restore fiscal discipline? The other is whether the country will end up with a better designed tax structure. The first matters a lot to the rest of the world. The US will account for roughly one-third of the incremental demand added to the world next year. So if growth were halved by a botched fiscal deal that would deal a real blow to global demand, which we would feel here. But if Congress were to reach agreement for a five-year plan to balance the budget, it is possible that the boost to domestic confidence would more than offset the mechanical hit to demand from fiscal tightening. Instead of the country growing at the 2 per cent generally expected, it could end up picking up some pace. The second matters more to the US itself. Its domestic market is so huge that it can, to some extent, get away with a poor tax system. But one effect has been for American companies to move activities, make profits, and hold cash balances offshore - and not just in the tax havens that we've been hearing so much about. Another effect has been to exacerbate inequalities in the US itself, as wealthy individuals can minimise their tax payments by using the loopholes that the system has deliberately created. Whether Congress has the ability to reach agreement on substantive reforms is another matter, but if it does, that would have knock-on effects on the rest of us. So what should we look for today from Mr Osborne? The headlines will be about the effort to get more money out of higher earners, the Coalition's "growth strategy," the holding off of fuel duties and so on. This is mostly about politics. But I would focus on two other areas. The first is the Office for Budget Responsibility's economic forecasts and, in particular, anything that goes any way to resolving the puzzle as to why this recovery has been by far the best in terms of employment compared with the early 1980s and early 1990s, but by far the worst in nominal GDP growth. The second area will be the detail of the deficit. Where are tax revenues falling short? Where does the Government plan to cut spending? Remember to ignore the transfer of the Post Office pension fund assets to the Treasury and the transfer of the interest paid to the Bank of England's holdings of gilts. There are different views about the sleight of hand here, for they make the numbers look better but change nothing. And remember this number: £120bn. That's what Britain has to borrow this year. The deficit-cutting programme has only just begun.