We now finally know who the presidential nominees of our two major political parties will be this fall. Republicans and Democrats stand opposed to one another on a range of policy issues. As a historian who studies national identity in multiethnic societies like ours, I am especially concerned by the growing divide between the two camps. Increasingly, some very conservative political figures describe Americanness in starkly different terms than do moderates and liberals.

The question of our national identity is not determined by specific legislation, although laws play a role in drawing the boundaries of who wins wide acceptance as a member of the American community. How we define Americanness is much more a matter of consensus, of broadly embraced terms, of offering inclusion, and seeing that offer reciprocated as mutual bonds turn a population into a people.

The 2010 census documented demographic trends that have been noticeable for a long time. In the future our country’s population will consist of ever-greater numbers of Asian and Hispanic Americans. But this itself is nothing new. At the turn of the last century some feared the huge influx of non-Anglo-Saxon European immigrants, people, some said, who could never be truly American. Such fear of “outsiders” and “unassimilable” immigrants or racial minorities has long haunted our politics.

Whether old or new, political rhetoric that labels some Americans as outside the bounds of the national community because of who they are is clearly exclusionary. Such tactics today play on the anxiety people feel about the social and cultural changes reflected in the recent census, and how these changes will affect the way we understand what it means to be American.

Barack Obama has long spoken of our national identity in terms that include Americans of every religious tradition, region, ethnic background, and sexual orientation in what he has repeatedly called the “American family.” The president has focused specifically on invigorating national bonds that unify Americans across ethnic lines. Even in his most populist recent speeches about the need for higher taxes on the wealthy, Obama has never even hinted that they are somehow “not American.”

On the other hand, there is the signal example of exclusionism coming from a leading conservative. In 2008 Sarah Palin declared: “We believe that the best of America is in these small towns that we get to visit, and in these wonderful little pockets of what I call the real America. ... This is where we find the kindness and the goodness and the courage of everyday Americans.” Palin here divides our population into those who live in “small towns,” folks who are disproportionately white, Christian, and culturally conservative, and those who do not. Members of the first group are “everyday Americans” who live in “real America.” The rest of us are, well, not.

Romney’s competitors for the Republican presidential nomination have used similarly exclusionary language to define President Obama as “not American.” Rick Santorum proclaimed: “Obama is detached from the American experience. ... He just doesn’t identify with the average American because of his own background—Indonesia and Hawaii.” Newt Gingrich characterized Obama’s worldview as “Kenyan.” Romney himself made a remark that a New York Times editorial called “close” to as bad as Gingrich’s when he asserted: “I don‘t think [Obama] understands America.”

And then there’s Ted Nugent, whose endorsement Romney actively sought and received after calling the aging rocker in March. Nugent recently referred to the Obama administration as “vile, evil, America-hating.”

To his credit, John McCain has repeatedly rejected the “othering” of Obama, as did Jon Huntsman. Such language is by no means universal among Republicans. As the newly-minted standard bearer of conservatism, Mitt Romney must publicly declare whether he accepts or disavows the exclusionist definition of Americanness reflected to varying degrees in the above remarks. The American people deserve to know what kind of Republican Governor Romney is, and what kind of Republican Party he wants to lead. Does he believe that President Obama “hates America”? Does he agree with Sarah Palin about who is a “real American,” and thus about the definition of our national identity?

Many Americans—in particular those who are white and middle-aged or older—remember growing up in a far more homogeneous place than the present. The sense of mourning for — and the desire to restore — that world is powerful, as is the fear of what is to come in the new, far more diverse America. The question is whether politicians choose to exacerbate that fear through divisive rhetoric, or to assuage it with language that seeks to unify us as Americans and encourages us to transcend our differences. Mitt Romney must openly declare which kind of politician he is.