John Feehery, a GOP consultant and former communications director for Speaker Dennis Hastert, says that the sleeper issue of 2008 may be violent crime. More precisely, it may be a sleeper issue in GOP-leaning districts. Feehery points out that while crime is down nationwide, it's up in smaller cities--and sentiments about illegal immigration may be tied in with worries about crime:

I have had a working theory for quite a while that the anger towards illegal immigration is only partially explained by job security. The biggest reason that many Americans dislike illegal immigration is a fear of crime.

The Democrats now sense this and are outbidding the White House on spending for immigration enforcement, with a special emphasis on deporting people convicted of major drug offenses and violent crimes. 
According to one news report, “A Homeland Security budget bill now moving through the House Appropriations Committee specifies that at least $800 million be spent after Oct. 1 to identify and remove the most violent and dangerous criminals from the U.S.”

Politico has more about the move by moderate Democrats--i.e., Democrats in Republican-leaning districts--to move to the right on immigration. How real is the anxiety about crime overall? Polls of Americans' top priorities generally no longer even list crime as a possible response. But in one recent poll where it did appear as an option--Gallup's poll in March--49 percent of Americans said crime and violence is something that they personally worry about "a great deal," putting it behind only Iraq and health care as a priority.