Imagine British Prime Minister Gordon Brown visiting Mexico, where he proceeds to extol the relationship between London and Mexico City. Although Mexico is suffering through internal difficulties, he lauds its role as a regional leader. And he concludes his remarks by urging the United States to bring Mexico into the American union—in essence, to add political equality and free immigration to the open market created by the North American Free Trade Agreement. After all, he explains, the United States and Mexico have much in common and union would strengthen American as well as Mexican institutions.

Officials in Washington, D.C. would not likely be amused. Indeed, they probably would inform the British foreign secretary that who the American states invite to join their political compact is a matter for Washington, not London. Maintaining a bare patina of diplomatic civility, the secretary of state likely would suggest that Great Britain butt out of America’s affairs, especially controversial political disputes.

For this reason, Prime Minister Brown is unlikely ever to make such a trek to Mexico City. No more likely to go is French President Nicolas Sarkozy or German Chancellor Angela Merkel. But President Barack Obama went to Ankara where he proclaimed that the European Union should add Turkey as a member.

“Let me be clear,” he told the Turkish parliament:

the United States strongly supports Turkey’s bid to become a member of the European Union. We speak not as members of the EU, but as close friends of Turkey and Europe. Turkey has been a resolute ally and a responsible partner in transatlantic and European institutions. And Turkey is bound to Europe by more than bridges over the Bosphorus. Centuries of shared history, culture, and commerce bring you together. Europe gains by diversity of ethnicity, tradition and faith—it is not diminished by it. And Turkish membership would broaden and strengthen Europe’s foundation once more.

All this may be true—though lauding a “shared history” involving several wars might not be wise—and the argument is not new for Washington. The United States long has viewed Turkey as a critical ally, anchoring NATO’s eastern flank, deterring Soviet expansionism southward during the cold war, and improving Washington’s relations with the Muslim world. So in America’s view, European acceptance of Turkey is a small price for someone else to pay to advance our agenda. Previous administrations have been no less vocal in their support for Turkish membership.

It’s a reasonable argument. But it isn’t Washington’s decision.

The European Union is a unique organization. It began small, focused on coal and steel, and evolved into a large-scale open market. Since then it has been transformed again, moving from developed west to underdeveloped east, and turning toward political as well as economic consolidation.

Up till now, at least, the EU has promoted economic growth by linking twenty-seven nations together in a larger market and squeezing out many of the inefficiencies created by national economic regulation. But Brussels increasingly is micromanaging more than member economies, transforming culture and politics as well.

Even now European states are struggling with the impact of increasing Muslim populations and a growing influx of workers from the new, poorer members of the EU. France and Germany are particularly wary of further EU expansion so long as workers are free to move freely throughout the continent. Whether such concerns are warranted or not from America’s perspective is not the issue. Membership in the EU means much more than just increased trade. It means societies changed in unpredictable and ever more unpopular ways.

Turkish membership would have an even larger impact on the organization. Large, poor and Muslim, Turkey claims European status only on the basis of propinquity. In terms of development, culture and religion, Ankara differs substantially from the rest of the continent.

Of course, that doesn’t mean Europe wouldn’t benefit from Turkey’s inclusion. But it means that there would be costs too, resulting in a complex balance to be struck. A balance that only Europe can make. Under the circumstances, French President Sarkozy was surprisingly restrained when he responded to President Obama’s remarks: “I have been working hand in hand with President Obama, but when it comes to the European Union it’s up to members states of the European Union to decide.”

Of course, the EU members should consider the larger geopolitical issues at stake. A pro-Western Turkey yields obvious strategic benefits. It helps counterbalance less friendly and more dictatorial Middle Eastern states. Ankara’s friendship with Israel, though recently strained, gives the latter more room to maneuver. A liberal democratic Turkey, along with Indonesia, is an important symbol to other Islamic states looking for a way out of oppression and dictatorship. All these ends are advanced by drawing Ankara westward in orientation.

Which is why Washington so fervently supports Turkey’s entry into the EU. And the U.S. government has a perfect right to make its views known across the continent. But such opinions should be shared privately with European governments, not proclaimed publicly to Turkey. After all, the benefits from Ankara’s membership are speculative, especially since Turkish public opinion has shifted against America and Europe. Most important, it is European, not American, society which would be transformed, perhaps dramatically, by EU expansion to Asia Minor.

Like his predecessors, President Barack Obama believes that the United States is anointed to lecture the rest of the world on subjects big and small. It’s time for some of the “change” that the president promised: more humility in Washington. Whatever American policy makers believe to be good policy, Turkish membership in the EU is up to the Europeans, not the United States.