The explosive issue of immigration is poised to creep back into the Republican primary battle as the candidates prepare to barnstorm South Carolina, one of a handful of states being sued by the federal government for their illegal immigration crackdowns.

While the issue played second fiddle to concerns like jobs and foreign policy in the prior two contests, voters in South Carolina are likely more attuned, given the high-profile lawsuit filed by the U.S. Justice Department.

"That's very much an important issue in South Carolina," said Van Hipp Jr., former chairman of the South Carolina GOP and current chairman of the advocacy group Americans for Securing the Border.

Mitt Romney is charging into the state with arguably the most aggressive message, praising the state's immigration law while trumpeting his own bona fides on the issue.

In a well-timed announcement, the Romney campaign on Wednesday rolled out an endorsement from Kansas Secretary of State Kris Kobach -- the co-author of illegal immigration laws in Arizona and elsewhere. Romney said he wants to work with Kobach to "support states like South Carolina and Arizona that are stepping forward to address this problem."

The campaign also released a statement from Kobach saying Romney would stand "shoulder to shoulder" with states like South Carolina in the illegal immigration fight. Kobach called Romney "the candidate who will finally secure the borders and put a stop to the magnets, like in-state tuition, that encourage illegal aliens to remain in our country unlawfully"...