[TBP]

I think they underestimated Cruz’s ability to turn out new voters.

And perhaps overestimated Trump's.

There could also be a bit of "confirmation bias" in the poll numbers -- pollsters hearing what they expected to hear, and reporting it.

[lentulusgracchus]

And perhaps overestimated Trump's.

Trump's younger voters didn't show in the proportions the older voters did. Oh, they meant to go .... then Ginger and Bennetta walked by. Oh, well, save the Republic another day, it'll still be there.

[xzins]

Yep. All of those.