Come May 2012, President Obama will welcome world leaders to Chicago, as the windy city plays host to the NATO summit. Heads of state and government from 28 nations will gather in Mr. Obama’s backyard.

Some of the issues topping the NATO agenda—not least of all Afghanistan--will also figure in the U.S. presidential election, Perhaps that is why the Administration is giving every impression that the NATO summit will be nothing more than a pit stop on the President’s 2012 campaign trail.

But that’s no way to treat friends and allies. Moreover, there is serious business to be done at the summit. As then-candidate Barack Obama once told then-candidate John McCain, the U.S. President has to walk and chew gum at the same time. Although the next election threatens to be a bruising one, Mr. Obama still has presidential duties to carry out.

The administration has a real opportunity to advance American leadership at the summit. Enlargement of the NATO alliance has been a sorely neglected topic in the past two years. President Obama must seize the moment and recommit the alliance to keeping its doors open to would-be members who have earned their place in the Euro-Atlantic family.

Ensuring that Macedonia joins NATO this year would be a sign that President Obama genuinely understands America’s primary role in creating and maintaining a democratic global order.

In 2008, the Greek government unilaterally vetoed Macedonia’s accession to NATO. That action broke with an age-old principle that NATO members do not play out bilateral disputes within the alliance. Last month, the International Court of Justice ruled that Greece had violated international law with its veto, since Athens had explicitly promised to not prevent Macedonia’s integration into Europe in an interim accord they signed with Skopje 13 years earlier.

But Athens vetoed Macedonia’s membership of the alliance regardless, and the Greek government has continued its vendetta against Skopje ever since. Worse, it has done so without a squeak of protest from the White House.

NATO’s cynical acquiescence to this type of bullying must end. Although it is a small country many miles from Washington, Macedonia still matters to the U.S.—and more importantly, to America’s commitment to the freedom, democracy and national sovereignty of fledging states.

International observers did not give Macedonia much of a chance when it emerged from the breakup of the Yugoslav Federation in the 1990s, but its progress has been incredible. In 20 years, Macedonia has evolved from a Balkan powder keg into a net exporter of security, providing the fourth-largest per capita contribution to NATO’s mission in Afghanistan (even though it is not even a member of NATO). Macedonia even contributed to the war in Iraq, where their combat troops fought side by side with American troops on the ground. And British Prime Minister Tony Blair publicly thanked Macedonia for providing a safe refuge for hundreds of thousands of Kosovar refugees during the Balkan wars of the 1990s.

By all objective standards—and by NATO’s own admission—Macedonia has fulfilled the alliance’s membership criteria. But Greek obstructionism means that NATO’s door remains closed. Ultimately, however, it is the willingness of NATO leaders to play along that has allowed Greece’s unconscionable stance to prevail. It is time for President Obama to exert leadership on this issue.

In the last few years, no country has benefited from the hand of international friendship more than Greece. Without global financial support—including tens of millions of dollars from the U.S. via the International Monetary Fund—Athens would not even be able to pay its bills. The days when NATO nations should feel constrained to let Greece indulge in regional obstructionism are long gone.

In May, President Obama will have a chance to stand not just for what amounts only to fair treatment of Macedonia, but for something far more important: the vision of a Europe whole, free and at peace.

Sally McNamara is Senior Policy Analyst in European Affairs at The Heritage Foundation.