Ann Coulter believes that presidential candidates who talk about border security but won't commit to building a wall along the U.S.-Mexico border are not serious about solving the illegal immigration problem.

"How many immigrants are enough?" Coulter asked on "The Kelly File." "We have 42 million now. 100 million? 200 million? How many are enough?"

Coulter said that she liked Mitt Romney's solution to the illegal immigration problem: Force U.S. businesses to use E-verify, which will cause undocumented immigrants to self-deport.

"We didn't round them up to get them here," Coulter said. "They're going to go home the same way they came."

Watch the "Kelly File" clip above.

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