The most serious threat to the government is now one over which it has minimal control — the deteriorating global economic environment, and particularly the possibility of a recession in the United States, now priced by leading US economists at 50% (Martin Feldstein, Republican-oriented) and 33% (Larry Summers, a Democrat).

Nearly all indicators from the US are turning down, except for the odd surprise such as new car sales. Friday night will see the July jobs and unemployment data released. A repeat of the terrible 18,000 net net jobs reported for June (or revisions that eliminate them) will send the US markets and sentiment plunging. Already American economists and the Fed see the US economy trending lower than it was at this time a year ago. It rebounded solidly in the final six months, and that’s what everyone is hoping will be repeated in 2011.

That includes those in Washington who thought the debt ceiling deal was done and dusted. The debt ceiling deal is based on growth this year of 3.1%. So far its running at 2.3% and easing. Cullen Roche, of Pragmatic Capitalism, produced a dire chart of  how bond markets have anticipated US slowdowns before and are saying exactly that again.

But worse, this time there’s no capacity for US policy makers to respond effectively to the US’s anaemic growth, even if it turns into a full-blown recession. Indeed, there is not the will to do so. Having spent a decade avoiding the issue of fiscal discipline, the American polity has decided the cusp of recession is the time to engage in a fiscal consolidation — an approach that, as Paul Krugman notes, may well exacerbate, not repair, America’s fiscal problems. The possibility of a political consensus on stimulus is, therefore, remote to nil.

The Federal Reserve, too, has few options, given how low interest rates remain beyond a further round of quantitative easing. The only possible significant shot in the arm for an ailing America is a significant fall in the US dollar to drive exports — including to Australian online shoppers eager for a bargain.

Even without their own home-grown, slow-motion financial crisis, the Europeans are in a similar position outside Germany: poor growth and neither the fiscal resources nor the political will to engage in stimulus. And the British have embarked on a fiscal consolidation of their own, despite their economy flat-lining. The Europeans don’t even have a declining currency to fall back on.

We still have China and Japan (more important than China in terms of trade surplus) and growth is mixed, rather than flat, but the RBA was right on Tuesday to focus overseas — more so than most commentators seem to understand — and worry about the conditions the economy is sailing into. The US and Europe in particular are worrying the RBA more and more. Unlike forecasts by economists like Westpac’s Bill Evans, the RBA will cut rates not because of a weak domestic environment, but because the external outlook has turned so gloomy that it needs to start protecting the Australian economy against a global crunch.

We will know more about the RBA’s latest thinking at 11.30 am tomorrow when the third Statement of Monetary Policy emerges from Martin Place, replete with updated inflation and growth forecasts for this year, 2012 and rough estimates for 2013.

A US recession and a global downturn — softened only by the speed with which China is switching from exports to domestic demand — would wreck the government’s return to surplus next year. Our revenue base is more exposed than ever to falls in corporate earnings, and heavily reliant on mining and finance industry earnings. A severe enough slowdown, and the question of a return to surplus will be off the agenda for years. The issue may well be whether there’s any political will for stimulus. Joe Hockey last night said the Coalition didn’t have an in-principle objection to fiscal stimulus but it tried to block the second round of stimulus in 2009 and, given Tony Abbott’s performance since then, the likelihood of support for another round looks remote.

Fortunately, Australia has something neither the US nor the Europeans have, and that’s considerable room to move on interest rates in the event a significant downturn means the job becomes one of stimulating the economy.

But in that eventuality, the government will face significant pressure to delay the carbon pricing scheme until economic recovery has re-started. Indeed, it would be all but impossible for the government to weather the storm of hysteria that greets the introduction of a new tax while the economy was flat-lining. For that matter, its whole strategy of taking hard decisions early in its term and using the final two years to bed them down and deliver a surplus would be wrecked, albeit for no reason within its control.

Labor would have been mugged not once but twice by an external financial crisis, putting it one up on the Scullin government. Then again, Rudd Labor was at its best when it had to confront the GFC. Another crisis might bring out the best in the Gillard government. It could hardly makes things worse.