WASHINGTON (MarketWatch) — Today’s weak economic growth numbers were as predictable as they are disheartening — and the blame lies squarely with those who opposed the president’s American Jobs Act nearly a year ago, and have in fact opposed an array of sensible economic policies to expand public investments that create jobs and economic growth ever since President Barack Obama took office

But first, the “news.” The $15.6 trillion U.S. economy slowed in the three months through June 2012. U.S. gross domestic product, or GDP, the sum total of all goods and services produced by workers and equipment in the United States, grew at a 1.5% annual rate in the second quarter of 2012. We are growing, but slowing. And this must renew policy makers’ urgency for action to prevent our economy from dipping further.

U.S. growth slows in second quarter

Economists have known at least since last summer’s debt ceiling standoff in Congress that an economic slowdown was a high probability outcome if policy makers failed to reverse steep retrenchments in public investments that create jobs and strengthen growth. The tremendous uncertainty created by the political spat stalled private investment and hiring at the same time that public investments in education, infrastructure, and energy efficiency, and social safety net programs such as unemployment insurance were running to the end of their terms for many out-of-work Americans.

Back in 2011, the economy slowed to 1.3% growth in the third quarter from 2.5% in the second quarter as that year’s debt-limit fight further unsettled skittish businesses and left consumers questioning whether lawmakers could be trusted to take the right policy actions to ensure a strong American economy. Nonresidential business investment growth slowed a year ago from double-digit growth in early 2011 to less than 10% in December, 8% in the first quarter of the year and just 5.3% in today’s numbers.

This is why Obama proposed the American Jobs Act in September. This would have strengthened the economy through job-creating and growth-enhancing public investments in education and transportation infrastructure, and by providing support for those most vulnerable and hit hardest by economic pressures. The forecasting consultancy Macroeconomic Advisors and economists at Goldman Sachs estimated last September that the American Jobs Act would increase GDP by an additional 1.5% and create an additional 2.1 million jobs. Moody’s economist Mark Zandi warned, “If policy makers do nothing, the odds are very high we’ll go into recession next year.”

And Congress accomplished next to nothing. Senate conservatives filibustered key elements of the proposal, and the Republican-controlled House of Representatives voted 33 times for a deficit-increasing repeal of health-care reforms, but not once on a credible policy to spur jobs and growth. Meanwhile, the federal government continues retrenching public investments and services that stopped the recession and made a down payment on economic recovery, and state and local governments have cut purchases and investment for 11 straight quarters now. The public sector — one-fifth of the American economy — is in a policy-made economic depression.

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Even worse, the deal emerging from last summer’s debt limit fight bound policy makers in a suicide pact that, with other scheduled cuts, will lead to a 1.3% economic contraction beginning Jan. 1, 2013, unless lawmakers can agree not to. As we tick closer to this “fiscal cliff” time bomb, the specter is already haunting businesses who might otherwise hire workers and increase investment.

Now here’s the good news. There’s a lot we can do to change this situation, and our private economy is carrying more momentum than headline numbers indicate. Though slipping to just 2.1% growth this quarter, the private sector has averaged 3% annualized growth since the U.S. economy began expanding again in June 2009. Though slowing, business investment still expanded in 9 of the 10 last quarters. America’s businesses are ready for business if they can be certain of sufficient demand from customers.

Indeed, the U.S. economy might muddle through if not for the global economic environment deteriorating rapidly, which is exacerbating the negative effects of our own too-rapid retrenchment of public investments. The United Kingdom and European economies, who lead us in the move to fiscal austerity, are already entering recession. The U.K. economy contracted at a 2.8% pace in this quarter, and Germany and France flat-lined in the first quarter, growing at 0.5% and 0% respectively.

U.S. policy makers should note this handwriting on the wall. Export growth, which helped lift the economy from recession, will be harder to sustain as other economies slow and as drought in the U.S. drags on agriculture exports, which account for 11% of the total. At $600 billion, the already large U.S. trade deficit will likely grow larger in the near future.

World economic events may be out of our control, but policy makers have a choice to fix our economic situation at home. A sensible way to do this is to reverse the policy-imposed depression in public investments. There is no question that our young students need schools and quality teachers. There is no question that revamping America’s ailing infrastructure would boost business competitiveness. And as nearly 4 million mortgage refinancers know, with long-term interest rates near zero after inflation, there has never been a cheaper time to pay for such investments.

Congress still has the power to change this, should it choose, as well as the power to ensure that the long-term unemployed don’t lose unemployment insurance benefits when the program needs reauthorization in December. And the Federal Reserve, to its credit, is stepping hard on the monetary policy gas pedal to help get growth up and unemployment down — but is far from “flooring it.” Ben Bernanke and the Fed still have plenty of monetary policy tricks up their sleeve and, with inflation at 0% in June, have no excuse for not pursuing their maximum employment mandate more aggressively.

These measures can prime our economy, but we will not truly unleash America’s growth potential until we deal with the still lingering real estate debt overhang, modifying mortgages to relieve financial stress and keep families in their homes and keep payments flowing to financial creditors.

For those who doubt how policy action can help our economy, take the Obama administration’s 2009 restructuring of the U.S. auto industry, which prevented two Detroit automakers from shutting down. Growing motor vehicles production accounted directly for 9% of economic growth in the second quarter, after driving 36% of economic growth in the first quarter.

Like today’s GDP numbers, the outcome from not doing these things is predictable: more of the same and worse. The choice rests with policy makers in Congress, or if they fail to do the right thing, with voters in November.