Moderator Chris Wallace asked Trump and Hillary Clinton to detail their plans to secure the southern U.S. border, saying there is "almost no issue that separates" the two candidates more.
Trump said one of his "first acts" as president would be to "get all of the drug lords" out of the country.
"We have some bad hombres here, and we're going to get them out," Trump said.
The hashtag #BadHombre was trending on social media shortly after he made the statement. In Spanish, "hombre" means "man," but the way Trump used it could be interpreted as offensive or derogatory.
Clinton said she does not want to see undocumented parents separated from their U.S.-born children.
"We have 11 million undocumented people," she said. "They have 4 million American citizen children."
Clinton said that she was been for border security for years and that she voted for it when she was a senator for New York.
"My comprehensive immigration reform plan includes border security," she said. "But I want to put our resources where I think they're most needed.
Clinton said Trump "choked" during his visit to Mexico when he failed raise the issue of building a wall on the southern border with Mexican President Enrique Peña Nieto — a longtime campaign promise.