How far behind is Texas primary after SC?
I don't know. My memory of 2012 is already a bit fuzzy, but iirc, it was delayed that year from March to the end of April.
The GOP-e was complicit, as witness the quote by Romney, when someone asked him why he wasn't even making one appearance in Texas despite its being such a loaded State. Romney said, cynically, "They'll come to me when I'm the last man standing", viz., it was all over but the shouting and Texas finally got to vote after the race was over.
I like to think that it was that abusively instrumentalist attitude that cost him the election. The man was a tool, and everyone knew it by Election Day.