I believe that it’s important for Trump to show that he welcomes Cruz into the fold. If Cruz stabs him in the back, then it’s on Cruz..and Trump comes off looking like the champ that he is.
If Cruz does that, he will have destroyed his already sinking career. Furthermore, as President, Trump can further sand-bag Cruz’s future with a couple of phone calls. Teddy is so one dimensional, he doesn’t realize that actions have consequences.