Jen DiMascio Washington

President Barack Obama and Republican presidential nominee Mitt Romney are putting forward two very different visions for the Pentagon. But their respective policy differences pale in comparison to the economic and congressional headwinds that will confront the one who is elected next month.

The defense-policy contrasts between Romney and Obama are “important but not necessarily Earth-shattering,” says Michael O'Hanlon, a defense analyst at the center-left Brookings Institution. “You could almost imagine [Romney's proposal] as Obama 2009 versus Obama 2012 in terms of the range of debate over the proper future of our budget.”

Shadowing any promise or plan for defense spending is the possibility of an additional $500 billion cut to Pentagon spending should lawmakers fail to delay or prevent the deficit reduction penalty known as sequestration. If it happens, whoever wins in November will have to reassess his plans.

In the eyes of Obama, the military must share in efforts to reduce the deficit. But after slews of program cuts, the president is having difficulty persuading lawmakers to support the details of his fiscal 2013 budget—his first real reduction in Pentagon spending.

Romney aspires to spend $2 trillion more on defense over the next 10 years. But after former President Bill Clinton scoffed at the idea during his Democratic National Convention speech, Romney campaign advisers are describing that as a goal to be achieved over time, as the economy recovers. And O'Hanlon says that the spending gap may be far less than that—$500 billion over 10 years.

And even if sequestration is avoided, strain on the economy—and the defense budget—will remain. “Either new president is going to face very significant fiscal pressures from the debt that will put pressure on how spending is allocated,” says Nora Bensahel, a senior fellow at the Center for New American Security.

O'Hanlon and other analysts are characterizing Romney's call to spend 4% of GDP on defense as an aspiration rather than a campaign pledge. For 2013, the defense budget would return to the fiscal 2011 spending level, before Congress passed the Budget Control Act mandating a reduction in all government spending—including defense. The increase in spending would be phased in over time, explains Mackenzie Eaglen, a fellow at the American Enterprise Institute and adviser to the Romney campaign.