The current controversy over hordes of Hispanics coming over the border singing "The Star-Spangled Banner" in Spanish is only the latest rise of a tide that ebbs and flows in the United States at regular intervals.

The debate over whether those who come from "out there" to "in here" are to be welcomed or repelled illustrates a paradox at the heart of this national enterprise - at once America is a country of immigrants and a country threatened by immigrants.

"There is nothing new about the issue of immigration becoming a hot political topic," says Gary Gerstle, a historian at the University of Maryland, College Park. "There are points historically when it becomes a major issue and grabs the attention of the polity in a major way.

"From that viewpoint, it is not surprising that something like this is happening today," he says. "The United States has long insisted, on the one hand, with having a relatively open border but, on the other hand, with being concerned about the volume, manner and character of those coming across it."

It is hard to find a point in American history when this was not an issue.

"This goes all the way back to the beginning of the country," says Matthew Crenson, a political scientist at the Johns Hopkins University.

"There was a debate, in fact, between Alexander Hamilton and Thomas Jefferson in the early part of the 19th century," he says. "Jefferson argued that immigration was a good thing because it would bring people who would contribute to the economy of the new country, while Hamilton argued that it was a bad thing since it would threaten the distinctive Anglo-American culture of the country."

The immigrants Jefferson was backing were the so-called Scotch-Irish, the Protestants who ended up populating much of the South.

But Jefferson also had his problems with immigrants, an early example of the recurring issue of language.

"Benjamin Franklin and Thomas Jefferson were worried about German speakers," says Aristide Zolberg, director of the International Center for Migration, Ethnicity and Citizenship at the New School University in New York. "They thought the German language was different and would bring with it cultural antagonisms to what they were trying to establish as an American outlook."...