Former Trump aide Corey Lewandowski mocks immigrant child with Down syndrome The former campaign manager made sarcastic comments about the girl on Fox News.

Former Trump campaign manager Corey Lewandowski is facing backlash after he mocked the story of an immigrant child with Down syndrome in a Fox News interview about the Trump administration's "zero-tolerance" immigration policy.

Lewandowski, who was in charge of Donald Trump's presidential campaign from January 2015 to June 2016, made the disparaging comment on "The Story With Martha MacCallum" Tuesday evening. Fellow guest Zac Petkanas, a Democratic strategist and former Hillary Clinton aide, relayed a story about a 10-year-old girl with Down syndrome who was separated from her mother after they crossed the border illegally.

"I read today about a 10-year-old girl with Down syndrome who was taken from her mother and put in a cage," Petkanas began. But before he could finish, Lewandowski replied "Womp, womp" in apparent sarcasm.

Petkanas immediately took issue with Lewandowski, responding, "Did you just say, 'Womp, womp' to a 10-year-old girl with Down syndrome being separated from her mother? How dare you? How absolutely dare you, sir? How dare you?"

Lewandowski talked over Petkanas' response, saying, "What I said is you can pick anything you want; the bottom line is clear."

Lewandowski had said prior to Petkanas’s relaying the story of the girl with Down syndrome that "as soon as you cross the border illegally, you have committed an act which is a disservice to all of the people who have stood in line and waited to get into this country legally."

Host Sandra Smith then cut off the argument and steered the conversation back to immigration policy in general.

Lewandowski responded to the backlash this morning, criticizing the mainstream media and what he called "fake news."

"Lots of Fake News today,” he wrote on Twitter. “I mocked a liberal who attempted to politicize children as opposed to discussing the real issue which is fixing a broken immigration system. It’s offenseive [sic] that the MSM [mainstream media] doesn’t want to talk about the fact these policies were started under Obama,” which is a false claim the president has often repeated.

Petkanas was relaying a story told earlier in the day Tuesday by Mexican Foreign Minister Luis Videgaray, who condemned the separation of families in a news conference.

He described recent cases involving Mexican children, including the 10-year-old Mexican girl with Down syndrome who last week was separated from her mother after they crossed the border. He said the girl is in McAllen, Texas, while the mother was taken to a center in Brownsville, Texas. The father is a legal resident in the United States and they are trying to get them reunited, Videgaray said.

"Our consulate in McAllen is doing the gestures so that, in an immediate fashion, the girl is taken out of the shelter and is reunified with her father, who has the status of a legal resident," Videgaray said. "Of course, this case, in particular, we have pointed it out to the American authorities at the highest levels."

Videgaray called the policy of separating children from their families "cruel and inhumane" and said Mexico had a "moral responsibility" to speak out.

Among those who immediately condemned Lewandowski's comments was former Fox News host Megyn Kelly, who tweeted, "There is no low to which this coward Corey Lewandowski won’t sink."

ABC News' Kirit Radia, Sarah Shales and Meghan Keneally contributed to this report.