Ms Nielsen was widely criticised on Sunday when she tweeted that her department does "not have a policy of separating families at the border".
The DHS secretary says the separations are warranted in cases where the parents have broken USA law by entering the country illegally - and that what her agency is doing is no different from how the government treats parents who break any other laws.
President Trump on Twitter Monday echoed that point. Lindsey Graham (R-SC) and Ben Sasse (R-NE) and Rep. Mario Diaz-Balart (R-FL), or those out of office, like former First Lady Laura Bush. U.S. Customs and Border Protection falls under the umbrella of the DHS.
Moderate Republican Sens. Susan Collins and Jeff Flake demanded answers about the treatment of migrant families in a Saturday letter to the DHS and the Department of Health and Human Services.
Nielsen suggested that some immigrants illegally entering the US with children are not in fact families, and that those seeking asylum should go to official ports of entry instead of crossing the border unlawfully.
The guide sheet adds, "DHS and HHS can take steps to facilitate reunification with your child (ren)". Nielsen says agents are not acting cruelly, but are enforcing the laws passed by Congress.
She challenged members of Congress to pass legislation if they want to see a change, even though the increase in forced family separations was set in motion by an executive action implemented by the Justice Department and Department of Homeland Security.
"If you are seeking asylum, go to a port of entry", Nielsen said. We operate according to some of the highest standards in the country.
Nielsen claimed this policy is in place not as a deterrent to keep families of immigrants away from the border, as other administration officials have said, but rather as a means of keeping the children safe.
Nielsen argued that some children are separated from their parents when they fail to provide documentation proving the familial relationship.
Hours after Trump's comments, the White House issued a statement saying the president had misspoken.
Earlier Monday he tweeted: "It is the Democrats fault for being weak and ineffective with Boarder Security and Crime. Don't wait until after the election because you are going to lose!"
The President underwrites this practice, and so does every single Republican in Congress who isn't calling for Sessions to stop prosecuting border crossing as a criminal offense. In the last two months, there's been about 2,000.