Some illegal aliens are "animals" or what the bible would call "lewd fellows of the baser sort" or "brute beasts". Rapists, murderers, and child molesters can be called "animals" and rightly so.
I find it difficult to believe that the president, or anyone, would call all illegals "animals". Perhaps your hatred of Trump has led you to misquote him. One should be careful as emotions and self-righteousness can lead to inaccuracies.