Texas doesn't have to go to war in the traditional sense.
They do what they can on non-Federal land. Texas officials can enforce state public safety laws. But, the best thing to do, is to bus the migrants to Dem Sanctuary Cities and States.
Texas needs to transform its Border Problem into America's Border problem by exporting that problem to non-Border states.
So far, the Feds haven't been reimbursing state and municipalities for the costs of taking in the illegal migrants. Biden's policies are draining state and municipal resources away long-time residents to deal with the illegal migrants. Voters in Dem jurisdictions see their needs being ignored to take care of the illegal migrants. More voters in Dem strongholds are willing to consider voting for non-Dem alternatives or not showing up at the polls for Dems.
If the Feds won't keep illegal migrants from entering Texas, there's no law against Texas sending them elsewhere voluntarily. Busing illegal migrants up North is working. It is eroding local and state support for the Biden Administration.
If the GOP had better quality candidates, it could better capitalize to strengthen majority in House, gain majority in Senate, and possibly defeat Biden.
Keep sending those migrant buses, planes, trains, boats, and zeppelins up North.