As usual, Dan Balz has the shortest and most cogent summary of the 2012 presidential race: President Obama’s real opponent is the economy. By that measure, Obama had a bad Friday, as new economic numbers confirmed that job growth is slowing.

If this trend, now in its third month, continues, the unemployment rate will likely go up; it actually dropped last month as another group of the unemployed quit looking for work, hardly a reassuring result. If in November, unemployment has gone up to 8.5 percent or higher, then I think Romney wins, perhaps comfortably. If, however, we stay in this muddle, where growth is slowing but not stalling, and unemployment stays about where it is today, we will have the very close election predicted all along.

But whoever wins will inherit a weak economy, perhaps on the verge of another encounter with the cliff. What will they do? If you are as interested in this question as I am, I recommend reading Paul Krugman’s recent article. Krugman is a broken record I actually like listening to. Since the beginning of the Obama administration, he has argued repeatedly that the United States and Europe are committing economic suicide by embracing fiscal austerity instead of stimulus. When the Obama stimulus was first debated, Krugman warned it was too small and has watched with horrified incredulity as elites of both parties have ignored the jobs issue and focused almost exclusively on deficit reduction.

His new article contains some interesting new data on the correlation between government spending and job creation, but Krugman’s argument is as old as Keynes. When the economy is underperformed and monetary policy is spent, the only lever left is government spending. Without it, not only do the unemployed — now some 12.5 million people — suffer, but the deficit will continue to grow as tax revenues shrink and transfer payments increase. So we are currently pursuing a folly: trying to cut our way out of an investment deficit.

I have always found Krugman persuasive. He comes from the “walk and chew gum” school of economics. We need to invest now, and once growth returns, address our structural deficit then.

The idea that government is the only institution that can lift our economy out of depression was once orthodoxy. Today, it is politically, but not economically, discredited. Evidence A is the Obama stimulus plan which, despite being oversold and underfunded, was successful in triaging the economy. But hard to make that case, as Obama well knows.

But perhaps Krugman’s best advice isn’t economic; it’s political. The right policy is worth pursuing anyway, he argues, and in this case may be more popular than elites believe. He notes that Obama’s jobs offensive this fall and winter went well, at least in the polls.

What choice does Obama have? Hunker down and hope unemployment improves a tick and that a negative campaign gets him a razor-thin win? Or take it to Romney with a real jobs plan? It might not work, but wouldn’t it be better to fight for something the country desperately needs?