I suspect foul play.
I actually don’t. I think Trump has made a very strong play for the politically ignorant and unmotivated, ... people who have been too angry to give a crap. Meanwhile Cruz is lawyerly in a way which turns off some, but is craved sustenance to the politically active. So when you do a poll, you get loads of people who simply see Trump in the news every day and know that liberals hate him. (Let’s not forget that 50% of Americans don’t know who Joseph Biden is, let alone Ted Cruz.)
Normally, pollsters can tease out the inactive by demographic inference, but Cruz and Trump appeal to a people who seem the same to demographers.
It’s just you’d think that some of these pollsters would learn from their mistakes!