I agree that Trump is the wall guy, but it is part of Cruz's immigration plan and he still has to get it out there because the press is not going to do it for him. Cruz was accused of flip-flopping on ethanol today even though he met with the press and told them exactly what he said today a year ago. He has to run ads to give his positions where the press runs with Trump's position for free.
I don't believe the polls that show close spreads or even Cruz ahead
There IS time, but the effort would have to be tremendous to even match the enthusiasm Trump has garnered