Texas should shut off all oil and natural gas leaving the state and cut electrical services leaving the state untill the feds act.
I certainly hope Texas law enforcement can secure our border without the help of militia. I am a fan of militia but history teaches us militia is undisciplined, unpredictable and prone to making well meaning mistakes. That said if the job is more then DPS and that Texas State Guard can handle then by all means call up the militia and let me know if they need a 66yo long time inactive Marine.
The oil and gas thing is doable, but not for very long. However long ago Texas decided it wasn't going to export energy via electricity, something to with taxes on the exported fuel, but not on the electricity, I think.
There are 3 major grids in the US. East, West and Texas. They are only lightly tied together. The links cannot support large amounts of power flowing across them, just enough to keep the systems synchronized, all on the same frequency, nominally 60 Hz. If there is a major loss of generation capacity, such as the gas fired generators being fuel starved, in the East and/or West grid, then Texas would have to disconnect completely, which interconnect breakers would do automatically anyway.