Why is Texas labeled as a "Deep South State"?

[hopper]

I don't get why Texas is seen by some as a Deep South State. It see it as part of the Southwest like Arizona, New Mexico, Nevada, and Colorado not like Arkansas, Louisiana, Mississippi, or Alabama which is Deep South territory. Does Texas's or Texas A&M's affiliation with the Deep South ly in College Athletics because Texas A&M plays in the SEC and Texas A&M and Texas played in the old Southwest Conference with South Carolina and Arkansas up to the early 1990's when both moved it to the Big 8 or Big 12? Is it because of politics because the state of Texas is a GOP stronghold along with rest of the Deep South States?