Trump is trying to win. He is going throw everything but the kitchen sink at Cruz. That is how it is done. Cruz is a big boy. He can take it. If Cruz gets the nomination, the Democrats and media will surely not shy away from this issue.
I think the big idea that Trump is planting the seeds of is the question of why, with hundreds of millions of eligible candidates born to American parents in the USA, we need to nominate a guy born to a Cuban father in Canada. Just as there must be candidates who are not named Bush or Clinton, one would think we could field a candidate born in the USA to citizen parents.
May be he is Castro plant.