You need to pay more attention. Almost every state bordering Mexico and several that aren't are backing Texas on the decision of opposing the federal branch on this. The Fed coming after Texas wouldn't necessarily mean secession either: that's why it would be a civil war, with much of the south joining Texas in their cause.

That is, if it goes that far to begin with. There's just no way Texas will be alone in their cause, whether you like their cause or not. They already aren't perfectly aligned with the fed, and there's no universe where every state is in alignment with the fed against Texas.