While the risk of a disorderly crisis in the eurozone is well recognized, a more sanguine view of the United States has prevailed. For the last three years, the consensus has been that the US economy was on the verge of a robust and self-sustaining recovery that would restore above-potential growth. That turned out to be wrong, as a painful process of balance-sheet deleveraging – reflecting excessive private-sector debt, and then its carryover to the public sector – implies that the recovery will remain, at best, below-trend for many years to come.

Even this year, the consensus got it wrong, expecting a recovery to above-trend  annual GDP growth – faster than 3%. But the first-half growth rate looks set to come in closer to 1.5% at best, even below 2011’s dismal 1.7%. And now, after getting the first half of 2012 wrong, many are repeating the fairy tale that a combination of lower oil prices, rising auto sales, recovering house prices, and a resurgence of US manufacturing will boost growth in the second half of the year and fuel above-potential growth by 2013.

Follow Project Syndicate on Facebook or Twitter. For more from Nouriel Roubini, click here.

The reality is the opposite: for several reasons, growth will slow further in the second half of 2012 and be even lower in 2013 – close to stall speed. First, growth in the second quarter has decelerated from a mediocre 1.8% in January-March, as job creation – averaging 70,000 a month – fell sharply.

Second, expectations of the “fiscal cliff” – automatic tax increases and spending cuts set for the end of this year – will keep spending and growth lower through the second half of 2012. So will uncertainty about who will be President in 2013; about tax rates and spending levels; about the threat of another government shutdown over the debt ceiling; and about the risk of another sovereign rating downgrade should political gridlock continue to block a plan for medium-term fiscal consolidation. In such conditions, most firms and consumers will be cautious about spending – an option value of waiting – thus further weakening the economy.

Third, the fiscal cliff would amount to a 4.5%-of-GDP drag on growth in 2013 if all tax cuts and transfer payments were allowed to expire and draconian spending cuts were triggered. Of course, the drag will be much smaller, as tax increases and spending cuts will be much milder. But, even if the fiscal cliff turns out to be a mild growth bump – a mere 0.5% of GDP – and annual growth at the end of the year is just 1.5%, as seems likely, the fiscal drag will suffice to slow the economy to stall speed: a growth rate of barely 1%.

Fourth, private consumption growth in the last few quarters does not reflect growth in real wages (which are actually falling). Rather, growth in disposable income (and thus in consumption) has been sustained since last year by another $1.4 trillion in tax cuts and extended transfer payments, implying another $1.4 trillion of public debt. Unlike the eurozone and the United Kingdom, where a double-dip recession is already under way, owing to front-loaded fiscal austerity, the US has prevented some household deleveraging through even more public-sector releveraging – that is, by stealing some growth from the future.

In 2013, as transfer payments are phased out, however gradually, and as some tax cuts are allowed to expire, disposable income growth and consumption growth will slow. The US will then face not only the direct effects of a fiscal drag, but also its indirect effect on private spending.

Fifth, four external forces will further impede US growth: a worsening eurozone crisis; an increasingly hard landing for China; a generalized slowdown of emerging-market economies, owing to cyclical factors (weak advanced-country growth) and structural causes (a state-capitalist model that reduces potential growth); and the risk of higher oil prices in 2013 as negotiations and sanctions fail to convince Iran to abandon its nuclear program.

Policy responses will have very limited effect in stemming the US economy’s deceleration toward stall speed: even with only a mild fiscal drag on growth, the US dollar is likely to strengthen as the eurozone crisis weakens the euro and as global risk aversion returns. The US Federal Reserve will carry out more quantitative easing this year, but it will be ineffective: long-term interest rates are already very low, and lowering them further would not boost spending. Indeed, the credit channel is frozen and velocity has collapsed, with banks hoarding increases in base money in the form of excess reserves. Moreover, the dollar is unlikely to weaken as other countries also carry out quantitative easing.

Similarly, the gravity of weaker growth will most likely overcome the levitational effect on equity prices from more quantitative easing, particularly given that equity valuations today are not as depressed as they were in 2009 or 2010. Indeed, growth in earnings and profits is now running out of steam, as the effect of weak demand on top-line revenues takes a toll on bottom-line margins and profitability.

A significant equity-price correction could, in fact, be the force that in 2013 tips the US economy into outright contraction. And if the US (still the world’s largest economy) starts to sneeze again, the rest of the world – its immunity already weakened by Europe’s malaise and emerging countries’ slowdown – will catch pneumonia.