American exceptionalism has become, as Karen Tumulty reports in the Washington Post, a frequently heard rallying cry for conservatives. The beating of the exceptionalist drum has a lot to do with attempts to discredit Barack Obama by suggesting—in the sort of respectable sounding language that an historian or social scientist might use—that Mr. Obama doesn't love or identify with the United States quite as much as the rest of us do. This suggestion is of a piece with the right jumping on Michelle Obama for her remark during the 2008 campaign about feeling really proud of her country for the first time.

Although the exceptionalist theme may partly be anti-Obama innuendo, innuendo works only insofar as it resonates with something larger and deeper. In the current case, that something is a strong—bordering on rabid—nationalism. Americans rarely label themselves as nationalists, but they exhibit to a remarkable degree the sort of attitudes that we don't hesitate to label nationalist when applied to foreign leaders, movements, or popular opinions. Against a strong nationalist backdrop, it has become de rigueur for American politicians to subscribe to exceptionalism. Mr. Obama's defenders, rather than criticizing the worldview of the exceptionalist drum-beaters, instead point out where the president himself has professed belief in American exceptionalism.

The United States clearly is like other countries in some respects and unlike them in other respects. Exceptionalism thus isn't of much use as an analytic construct. As a political phenomenon, the important question to ask about exceptionalism is what beliefs and attitudes it has tended to inculcate in Americans and what sorts of policies those beliefs and attitudes have tended to promote. While pointing out that I love my country as much as the next American, I also note that I am not a politician running for office and thus am free to note the downsides of exceptionalism. These are downsides not of any particular attributes of the United States, including ones that would tend to make this country exceptional. Instead, they are the downsides of Americans forming much of their worldview around the idea that the United States is different from, and better than, anyone else.

Exceptionalism has many negative effects. Here are some of the principal ones:

It encourages the mistaken belief that American values and political institutions, because they are deemed superior to anyone else's, will be readily accepted and understood by non-Americans.

It makes it difficult for Americans to see the negative sides of what many non-Americans see, fairly or unfairly, in the United States. It thus is difficult for Americans to understand anti-Americanism.

It encourages inconsistent one-way application of principles, which often provide another source of resentment of the United States. Americans see nothing wrong, for example, with rejecting having the International Criminal Court exercise jurisdiction over U.S. citizens while the United States asserts its own extraterritorial jurisdiction over many crimes that occur in other countries.

It leads to the mistaken belief the principles of international relations do not apply to the United States as they apply to other countries. Americans have a hard time understanding, for example, that other countries seeing the United States as threatening may start to act in concert against it.

It leads to the mistaken belief that the involvement of the United States is indispensable in many endeavors best left to others.

In general, it inhibits appreciation of the limitations to what the United States can accomplish. Those limitations may involve anything from U.S. military forces reshaping a foreign country to U.S. intelligence services trying to figure out what is going on in a foreign country.

All of these tendencies have gotten the United States into trouble—sometimes deep, very expensive trouble—and could do so again.

Nationalism always entails some perceptual and attitudinal blind spots, as we can readily see in the nationalism of others. What would make the United States truly exceptional is for it to become the first strongly nationalist country to recognize and overcome its blind spots.