Over the past twenty months, progressives, realists, and even some sensible conservatives have been disappointed by various aspects of the Obama administration's foreign and defense policy. Convinced that his election would mark a dramatic departure from the Bush administration's many missteps, they have been surprised and dismayed by Obama's increased reliance on drone attacks in Pakistan and elsewhere, his decisions to escalate the war in Afghanistan (not just once but twice), the retreat on Guantanamo, the Justice Department's use of dubious secrecy laws to shield torturers and deny victims the ability to sue them, the slow-motion reassessment of "Don't Ask, Don't Tell," the timid retreat from the lofty principles enunciated in his 2009 Cairo speech, and the unwillingness to consider anything more than trivial redutions in the bloated national security apparatus.

I share many of these concerns, but I don't really blame Obama. The buck may stop in the Oval Office, but it's not like he can simply wave a magic wand (or give another speech) and get the rest of the government to fall into line. Instead, the fact that U.S. foreign and defense policy hasn't changed very much reflects the powerful structural forces that inhibit any president's freedom of action. Or to put it more simply: he's trapped. Even if Obama wanted to chart a fundamentally different course (and I'm not at all sure that he does), he wouldn't be able to pull it off.

The first obstacle is America's current global position. Over the past sixty years, the United States built up a vast array of global military facilities, security partnerships, and overseas commitments. In the process, the United States ended up with the responsibility of providing a lot of collective goods (freedom of the seas, regional stability in Europe and Asia, security of global oil supplies, etc.) and it also ended up with a flock of client states who depend on us for various forms of economic, military, and diplomatic support.

These arrangements arose primarily due to the Cold War, but instead of dismantling them when the Cold War ended and returning to a more sensible and restrained grand strategy, the United States instead chose to expand its global responsibilities even further. This was partly because we didn't foresee any real opposition: as George H. W. Bush put it, we found ourselves "at the pinnacle of power, with the rarest opportunity to reshape the world." Hubris played a role too: U.S. leaders convinced themselves that we had the will and the skill to manage vast areas of the globe. Or as Secretary of State Madeleine Albright famously put it, the United States was the "indispensable nation" and that the U.S. "sees further than other countries into the future." And it was also because we thought that we could embed other countries into a set of rules and institutions that were largely of U.S. design. As Richard Haass, former director of policy planning and now president of the Council on Foreign Relations, declared in 2002, the goal was to integrate other countries "into arrangements that will sustain a world consistent with U.S. interests and values and thereby promote peace, prosperity, and justice."

So the United States expanded NATO deep into eastern Europe, adopted the foolish strategy of "dual containment" in the Persian Gulf, invaded Iraq in 2003 in a misguided attempt to transform the Middle East by force, and then got itself bogged down in a costly and ill-conceived effort at nation-building in Afghanistan. U.S. military forces remain deeply engaged on every continent, and as the Washington Post recently documented, the "war on terror" has led to a vast expansion in secret intelligence activities -- much of it conducted by a shadowy network of private contractors -- the scope of which is not even fully understood by the civilians who are allegedly in charge.

It is increasingly obvious that the United States has taken on a set of missions that it is not very good at, and that it cannot afford to continue without hollowing out its power here at home. It's also likely that some of these commitments are eventually going to go south (i.e., whenever we are propping up governments that lack popular support or that are pursuing policies that the rest of the world regards as wrong). The problem Obama faces, however, is that it would be neither easy nor cost-free to liquidate these commitments quickly. This is essentially a variation of the familiar "hegemon's dilemma": having occupied a position of primacy and taken on a vast array of global responsibilities, trying to disengage from them is like dismounting from a tiger. Once you begin to disengage, you may invite some short-term instability that actually makes things look worse. Moreover, any attempt to shift U.S. burdens onto others or to make significant cuts in our defense expenditures is bound to invite fierce opposition from the GOP, who would be quick to paint Obama as a cowardly or feckless appeaser. Instead of a long-overdue rethinking of U.S. strategy, therefore, we have a continuation of the status quo and an attempt to muddle through with our fingers firmly crossed.

The second impediment to change is the foreign policy establishment itself. As I've discussed before, the balance of political power inside Washington is heavily weighted towards the energetic use of American power -- and especially military power -- in virtually every corner of the world. Although think-tank denizens at Brookings, AEI, Heritage, and the Council on Foreign Relations sometimes disagree about specific policy initiatives, the vast majority are enthusiastic defenders of America's dominant global role. Hardly anyone at these institutions strays outside a rather narrow spectrum of thought, or questions the inherent legitimacy of the United States intervening just about anywhere it wants, even if the predictable results are the deaths of thousands of innocent civilians.

For the most part, debates within mainstream foreign policy circles run the gamut from A to B, from neoconservativism at one end and hawkish liberal interventionism at the other. As I said a few years ago, if neocons are essentially liberals on steroids, then most liberal internationalists are just kinder, gentler neocons. They agree on the virtues of American primacy, the need to prevent WMD from spreading (while keeping most of our own), the desirability of spreading democracy nearly everywhere, and the value of nearly all of the United States' current alliances. The only issue where neocons and liberals part company is the role of global institutions (neocons see them as dangerous constraints on U.S. autonomy, while liberals see them as useful supplements to American power). Given this basically bipartisan consensus, it is hardly surprising that most of the senior officials in Obama's foreign policy team were open supporters of the Iraq War, as well as steadfast believers in the United States right to intervene wherever and however it sees fit.

Ambitious foreign policy wonks understand that straying outside that comfortable consensus isn't going to advance their careers. That is why even sensible moderates have to polish their hawkish credentials if they want to be taken seriously, and even experienced pillars of the establishment are not immune from this same tendency. For example, the former president of the Council on Foreign Relations, Leslie Gelb, has admitted that he supported the Iraq War in 2003 in part to maintain his own bona fides within the establishment. In his words, "my initial support for the war [in Iraq] was symptomatic of unfortunate tendencies within the foreign policy community, namely the disposition and incentives to support wars to retain political and professional credibility" (emphasis added). And given that Gelb acted this way even though he was on the brink of retirement, you can imagine how more powerful this incentive is for someone starting out their career.

Finally, Obama clearly understands that the U.S. military has become a very powerful institution in American society, and that he doesn't have the personal background or clout to take them on directly. This situation helps us understand why he's gone slow on DADT, why he couldn't say no to their requests for more troops in Afghanistan, and why the Pentagon budget will continue to rise despite our massive budget woes.

In short, even if Barack Obama wanted to do many of the things that progressives might want, he would face enormous opposition from the uniformed services, the defense corporations who subsidize those conservative think tanks, the array of special interest groups pushing their own particular foreign policy projects, and the legion of hawkish pundits at Fox News, the Weekly Standard, and AM talk radio.

And let's not forget the true wing-nut elements in the American body politic. When both the secretary of Defense and our commanding general in Afghanistan have to waste precious time telling some obscure bigot in Florida that burning the Koran will put U.S. soldiers at greater risk, you know that the people who are allegedly running the country don't have much latitude to explore genuine alternatives.

In short, if you're disappointed that Barack Obama didn't live up to your expectations, you ought to go a bit easier on the poor guy. He can tinker at the margins, and he can probably resist the bad advice of those who'd like to get us into a few more wars (e.g., Iran), but he's not in a position to engineer a more thorough reassessment of our global strategy. Change will eventually come -- especially if the U.S. economy doesn't turn around and major deficits persist -- but it will be a slow and grinding process and an awful lot of money and more than a few lives will get wasted before we get there.

But don't lose hope entirely. As I often remind myself, it could have been a lot worse.