"We have presidential elections as a substitute for serious democratic politics" – that’s what Andrew Bacevich says. He’s been writing and teaching history and international relations at Boston University, after spending 23 years in the army and retiring as a colonel.

What would serious democratic politics look like? First of all, Bacevich says, we need a real debate about the idea of a global war on terror. Then we need a debate on what he calls our "empire of consumption."

"Obama and McCain agree on the global war on terror," he points out: McCain wants to fight it in Iraq, Obama in Afghanistan. "My own preference would be for an election in which we had one candidate making the case for the global war on terror – that would be McCain – but we would have an opponent who would make the case that the concept of global war as the response to violent Islamic radicalism is flawed. We ought not be in the business of invading and occupying other countries. That’s not going to address the threat. It is, on the other hand, going to bankrupt the country and break the military."

How then should we respond to the threat? Bacevich favors a "defensive" strategy of "containment." We need a president who acknowledges that it is not our job to "tutor Muslims in matters related to freedom and the proper relationship between politics and religion." He concludes, "Let Islam be Islam."

But he’s not one of those radicals who argue there is no difference between the Democrats and the Republicans. "I call myself an Obama-con, Bacevich says, "a conservative who will vote for Obama – because of the Iraq war. He has vowed that he will end the war and withdraw US combat forces. If he does that, it will render a verdict on the Iraq war: that it was a mistake and a failure. That verdict might open up the possibility for a debate about the fundamentals of US foreign policy. If McCain gets elected, the chances of us having that debate are close to zero."

We shouldn’t blame George Bush for the underlying assumptions of the global war on terror, Bacevich argues. "Really it was Bill Clinton who more than anybody else made armed intervention a routine aspect of American political life. Yes, George Hebert Walker Bush started the ball rolling with the overthrow of Noriega in Panama followed by Desert Storm followed by the intervention in Somalia. But Clinton picked up the baton in Somalia; Clinton went into Haiti; Clinton went into Bosnia, Clinton went into Kosovo, Clinton pummeled Afghanistan, Iraq and Sudan with bombs and missiles. So there’s blame to be shared by both parties."

But weren’t Clinton’s actions "humanitarian" interventions?

"And Bush overthrew Saddam Hussein because he wanted to liberated the Iraqi people," Bacevich replies. "When the US uses force, it advertises its purposes in idealistic terms. But the US does not use force primarily for the purpose of advancing democratic values or freeing the oppressed. The US, like every other power in history, uses its power in order to satisfy concrete interests."

And Democrats agree with Republicans on the "concrete interests" of Americans: preserving what Bacevich calls our "empire of consumption." (He borrowed the term from Harvard historian Charles Maier.) After WWII, the US was an "empire of production" – "we made the stuff that everybody else wanted." So the country did not go into debt. "But we have increasingly become a culture that emphasizes consumption – limitless consumption – regardless of whether we have the money to pay the bills, while others, notably China and Japan, have become the source of the goods we consume. There’s something fundamentally out of whack here. This disparity between what we produce and what we consume is simply not sustainable."

Neither Obama nor McCain, he says, realizes the seriousness of this problem of "limitless consumption." I asked whether any president in recent history had.

"Jimmy Carter," he replies. "His famous ‘malaise’ speech in 1979 was enormously prescient in warning about the consequences of ever-increasing debt and dependency. Carter’s argument was that energy independence provided a vehicle for us to assert control of our destiny, and to reassess what we meant by freedom: is it something more than simply consumerism?

"But that speech was greeted with howls of derision. Ronald Reagan said we could have anything we wanted. There were no limits. Then we the people rejected Carter’s warning and embraced Reagan’s promise of never-ending abundance. That was a fateful choice."

I pointed out that, at the Democratic National Convention, the Democrats said the same thing Reagan did. Hillary Clinton for example said "there are no limits to what is possible in America."

"That’s the language of American politics," Bacevich replies, "for both the mainstream left and the mainstream right. But that idea is not really sustainable when we look at the facts."

Andrew Bacevich’s new book is "The Limits of Power."