MESA, Ariz. (AP) - The Republican candidates say more must be done to combat illegal immigration.

The topic was a natural for Wednesday night's debate in Mesa, Ariz.

Newt Gingrich says he would devote as many resources as necessary to securing the U.S.'s southern border and that he would build two separate fences at the border to make it more difficult to cross illegally. He also says he'd send thousands more employees of the Homeland Security Department to border areas.

Mitt Romney says he would put more resources into securing the border and support programs that make it more difficult for illegal immigrants to work in the U.S. He says Arizona's approach to illegal immigration is a "model" for the country.

Rick Santorum says he would also beef up efforts to combat illegal immigration.