On Wednesday, Department of Homeland Security (DHS) Secretary Kirstjen Nielsen faced a tough line of questioning by House Democrats about the part she played in children getting separated from their parents at the border as part of Trump's zero-tolerance immigration policy.

While there were many moments during the hearing that caught Nielsen off guard, one back-and-forth, with freshman Rep. Lauren Underwood (D-Ill.), went viral for exposing the secretary’s ignorance surrounding the psychological and physical trauma experienced when children are separated from their families.

“Were you aware that the trauma of family separation is connected to something called toxic stress?” Underwood asked.

When Nielsen responded that she was unaware of the term, Underwood went on to explain that “toxic stress can actually change a child's brain because it's still developing” and “traumatic effects don't go away even if a child is reunited with their family.”

Although Nielsen admitted that she did not know “toxic stress” can also lead to physical ailments, like diabetes, she also tried to place blame on the children’s parents for taking them on to cross the border.

As a result, Underwood concluded that the DHS knew the possible effects of separating families but decided to proceed anyway.

"From what I’ve heard today, I’m not sure if DHS was so negligent that they didn’t know how traumatic family separation was for children, or if they knew and did it anyway," Underwood said. "But in my opinion, both are unacceptable. Tearing kids and their parents apart like this is immoral, ma'am, it's un-American, and it's just plain wrong."

After the hearing, Underwood tweeted more information about the harmful effects of separating families.

"Children detained at our border experience inhumanely low temperatures and are malnourished and caged," Underwood tweeted after the hearing. "Many have experienced abuse. All are now at risk for learning delays, mental health issues, and assorted illness. This health and humanitarian crisis is caused by our own government."

She continued, "Sec. Nielsen had few answers for me and showed herself to be uninformed on the impact of her Department's policies. That won’t fly anymore. To those in our administration who would harm children and families, I say: You answer to Our House now."

Underwood, a 32-year-old former nurse, is the youngest Black woman ever to be elected to Congress.