HOUSTON — Senator Ted Cruz cannot stop talking about the Alamo.

He is always eager to twang, delivering his best stump-speech impression of a West Texas farmer. He boasted recently that he knew how to “shoot me a bird.”

“I cannot wait to get home,” he told voters in Nevada, unsubtly, after a disappointing third-place finish in the caucuses there, “to the great state of Texas.”

Since announcing his bid nearly a year ago, Mr. Cruz has placed next week’s so-called Super Tuesday voting contests at the center of his plans: He would sweep through the heavily evangelical Southern primaries, advisers said, and run up the margin in his delegate-rich home state.

But as Donald J. Trump threatens to steamroller through the primary season, muscling Mr. Cruz and Senator Marco Rubio of Florida aside entering Thursday’s debate, there has been a reckoning deep in the heart of Cruz campaign headquarters: Texas could, for all practical purposes, be Mr. Cruz’s last stand.