• The US military has occupied vast stretches of the southern border.
• A Justice Department opinion allows military arrests outside designated zones.
• National defense areas cover one-third to one-half of the US-Mexico border.
• The military's role in domestic law enforcement is expanding.

The expansion of the military's arrest power at the southern border may indicate a shift in the administration's approach to immigration enforcement, which could have significant implications for the balance between national security and civil liberties. This development suggests that the military's role in domestic law enforcement may be growing, which could raise concerns about the potential for mission creep and the erosion of civilian authority.