Matt basically summed up the premise of Hannah Arendt's "Origins of Totalitarianism" with his comparison of the Apartheid Wall and Trump's Border Wall:

"The moment human beings lacked their own government and had to fall back upon their minimum rights, no authority was left to protect them and no institution was willing to guarantee them...

...The clearer the proof of their inability to treat stateless people as legal persons and the greater the extension of arbitrary rule by police decree, the more difficult it is for states to resist the temptation to deprive all citizens of legal status and rule them with an omnipotent police...

...The point is that a condition of complete rightlessness was created before the right to live was challenged...

...The more the number of rightless people increased, the greater became the temptation to pay less attention to the deeds of the persecuting governments than to the status of the persecuted...

...It is quite conceivable, and even within the realm of practical political possibilities, that one fine day a highly organized and mechanized humanity will conclude -- quite democratically --  namely by majority decision --that for humanity as a whole it would be better to liquidate certain parts thereof."

-- Origins of Totalitarianism,

The rhetorical escalation of Trump by constantly bringing up MS13 is designed to declare, openly, that one set of humanity is no longer worthy of the basic rights that should be guaranteed to all. By labeling one group as an enemy, over and over again, you lay the groundwork to go out and annihilate that group while declaring the slaughter to be an act of self defense. This is the logical conclusion of creating an oppressive physical barrier. It is to give the state the flexibility to label all of those on the opposing side as a dangerous hoard of brown people who must be put down with lethal force. It allows the occupying force to point to the conditions that THEY created as a just cause to put down their victims. By first priming a compliant and passive nation rhetorically to the dangers of the "other", we take an additional step toward allowing for the mass slaughter at a later date.