POWs do not need to be charged with a crime. Indeed, under international treaties and laws governing armed conflict, POWs generally can't be criminally charged for simply participating in hostilities.

They can be held without charge until the conclusion of hostilities. They are not entitled to the protections afforded to the accused, because they are not accused. They are not entitled to access to the criminal justice system.

By describing them as "invaders", he is suggesting that immigrants be treated as enemy combatants.