Can Texas jail illegal border crossers?

Question

From recent news: Texas Begins Jailing Border Crossers on Trespassing Charges (5 NBC Dallas-Fort Worth)

I was under the impression that immigration and border protection were the exclusive domain of the federal government. Was that incorrect?

Answer 1

This letter from the governor says what happened, at the level of "the state". First, this all relates to a series of proclamations, saying

that the surge of individuals unlawfully crossing the Texas-Mexico border poses an ongoing and imminent threat of disaster for certain counties and agencies in the State of Texas

This is the standard kind of gubernatorial proclamation that we are now familiar with from covid. The disaster proclamation from May is here.

The recent letter asserts a need for additional manpower to arrest those violating state law. The standard recitation of authority is

As “Commander-in-Chief of the military forces of the State” under Article IV, Section 7 of the Texas Constitution, the governor can “call forth the militia to execute the laws of the State.” Section 431.111 of the Texas Government Code likewise recognizes that the governor can call on state military forces “to enforce state law” and “to assist civil authorities in guarding [or] conveying prisoners.” And Section 437.002 of the Texas Government Code recognizes that “[t]he governor has full control and authority over all matters relating to the Texas military forces.”

The bottom line (and last sentence) is

I hereby order that the Texas National Guard assist DPS in enforcing Texas law by arresting lawbreakers at the border.

So actually, Texas increases the available manpower to enforce the law. Whether or not individuals engaged in such law enforcement are guilty of knowingly violating anyone's civil rights is a separate question. If and when there are actual prosecutions, we will be able to see whether the alleged violation of state law. The Texas criminal trespass statute, §30.05, does require that the trespasser "had notice that the entry was forbidden; or received notice to depart but failed to do so", so unposted land with no order to leave communicated is trespassable without criminal consequences.

Answer 2

The U.S. federal government has taken the position that this executive order is illegal and has plenty of precedent on its side. As of July 29, 2021:

U.S. Attorney General Merrick Garland told Abbott in a letter Thursday that the governor’s executive order “violates federal law in numerous respects, and Texas cannot lawfully enforce the Executive Order against any federal official or private parties working with the United States.”

Garland said the Department of Justice “intends to pursue all appropriate legal remedies to ensure that Texas does not interfere with the functions of the federal government” if Abbott does not rescind the order.

A lengthy analysis can be found in a reprint of a Congressional Research Service report, but the bottom line is that state and local government officials can only participate in immigration enforcement with federal authorization because immigration is the sole province of the federal government and state and local governments are otherwise not permitted to discriminate on the basis of national origin.