Poor management skills.
It shows in spades how totally naive Trump is about the system. Cruz has totally alienated fellow republicans by his bombastic ways. So was Trumps ego so large he did not think that Cruz was capable of doing something like that? If so, he does not belong in the White House. That could well be the case. We might hear something along that line in the next few days.
Jaws dropped all over town, and are still on the floor, when it was announced that Cruz was given a prime time speaking slot on a major night.The world knows what Cruz is capable of saying and doing. Cruz will be a problem for the republicans win, lose or draw going forward to 2020.
it is possible Cruz put those lines in the speech at the very last second. B ut t still Trump is the one who gave Cruz the speaking time. Exceedingly poor judgement by Trump.