In trying to explain the differences between the United States' southern and northern borders, Sen. Lindsey Graham (R-S.C.) found himself forced to make clear that he meant Mexico no disrespect.

"Why is one [border] a problem and the other is not? Because Canada is a place where people like to stay," Graham said. "We love to have them visit, they want to go home because it's a nice place. But people coming across the southern border live in hellholes. They don't like that. They want to come here. The problem is, we can't have everybody in the world who lives in a hellhole coming to America."

The difference, Graham said, is jobs. "They come from countries where they can't find work and life is miserable."

Sen. Jeff Sessions (R-Ala.), an immigration reform skeptic, quickly responded that "while there's poverty in Mexico and some really poor areas, it's not a hellhole. There are some great things going on in Mexico."

Graham replied: "You're right. I wasn't slandering Mexico, I'm just talking about all the places people want to leave, for whatever reason."

For the first time, more Mexicans appear to be leaving the U.S. for Mexico than the other way around, according to the Pew Research Center. But the number of border-crossers from Central American countries more than doubled last year, as people flee violence, crime and dim economic prospects.