In football parlance, Trump is creating a hole—clearing a path—for Cruz by defining and highlighting the hot button issues. If Trump can stay in the game, he might even win, but, given his lightening rod nature, that is against the odds.
I see Cruz and Trump as 2 halves of a whole. They seem to agree on many of the issues. Trump is the bombastic, un-PC half; Cruz is the subtle, more polished half. Both have the same or similar message. The difference is in how they convey it.