That’s the argument being made by Peter A. Brown, assistant director of the Quinnipiac University Polling Institute.

He says that immigration (like affirmative action 15 years ago) is the kind of emotional wedge issue that offers Republicans a way to split rank-and-file Democrats from their leaders in the 2008 presidential campaign.

Both issues, Mr. Brown says, have raised important challenges for presidential candidates, especially Democrats, as they craft their platforms. In both cases, key portions of the Democratic base — black voters on affirmative action and Hispanic voters on immigration — feel strongly about the issue and contrary to the general public.

That, he says, puts presidential wannabes in a tough position as they try to appeal to both their party base and the electorate at large.

Mr. Brown argues that a kind of consensus has been reached on affirmative-action policies that has led the issue to become less central in political campaigns. There seems to be broad agreement, he says, that colleges and employers should make special efforts to attract people from minority groups but not have lower standards for their admittance and employment.

But immigration, he says, remains a political hot potato. How the candidates fare among swing voters could be affected significantly by how the presidential contenders frame their stance on the issue.