The only power the feds actually have is "to establish an uniform Rule of Naturalization" and "shall protect each of [the states] against Invasion" and, after 1808, the power to prohibit "Migration or Importation of such Persons as any of the States now existing shall think proper to admit" (slaves).

Texas isn't deciding who can be a citizen or not, the only federal immigration rights explicitly mentioned are prohibiting people, and it's implied that the states get to choose who they want to admit. In fact I believe the constitution + amendments only prohibits states from refusing to admit citizens (under XIV).

The only constitutional avenue to strike this down is the "Rule of Naturalization", that it allows the government to force states to house asylum seekers and those who are being considered for citizenship - but that's clearly an expansive interpretation of "Rule".

Of course they don't care about what the constitution actually says, so I'm not trying to argue that the Texas law won't be overturned (it will) just that there's no basis for it.