The invading horde appears to be dirt poor, so their shoes are likely not in the best of shape from the beginning. How far can they walk before they start falling apart?

Reporter with horde in Mexico saying:

Yesterday, grueling 8 hour walk.

Today, seeing signs of fatigue, talking a day of rest.

One organizer passed-out on camera from heat.

If they are already in this shape, there is no possible way these people can make it even halfway across Mexico.