Canadian citizen held for months after border agents dismiss papers as fake
theguardian.com
theguardian.com
The abuse goes further. Both the U.K. (where it's explicit) and U.S. actively try to terrorize immigrants and create "hostile" environments for them. Terror cannot be a tool used by law enforcement for any reason (for one thing, it is "cruel", as in "cruel and unusual"), and it's also punishment without conviction.
Finally, these agencies' power is expanding. The DHS surveillance of all citizens was in HN recently, and I read another article where they claimed jurisdiction over all 'movement of goods' in the U.S. Note also that the expansion of DHS power coincides with the denigration the FBI, an agency rooted in the judicial process and rule of law (for example, they are part of and overseen by the Department of Justice).
The use of these agencies fits both the nationalism (hatred of immigrants) and authoritarianism of the right-wing parties.