Happily allow Texas to secede from the nation, seize all US government property and hope the newly-created country establishes its own military. Create tariffs making ANY trade with Texas so cost prohibitive that it has to buy its arms from China. Shrug our collective shoulders when Mexico declares war on the country of Texas. Scratch our heads when the country of Texas is returned to Mexico. People of Mayan, Olemec and Aztec descent, it should really go to you! Spain may not reclaim Texas for geopolitical reasons.
Grant any former U.S. citizen who is forced to become a citizen of the country of Texas assylum in Arizona. Require citizens of the country of Texas to supply valid birth certificates and Social Security numbers before entry into the US. Upon verification, deny entry.