I think Trump's comments on abortion really killed his electability, it will kill him with the woman vote and Cruz is not a viable alternative.
Honestly I think the republicans only shot at beating Hillary at this point is if they swallow their pride and form a Trump/Cruz ticket you need both bases on board to win.
The abortion comment hurt him some because it showed his lack of legs on that particular issue. People who have debated that issue for years know that yo cant turn the woman getting the abortion into the bad guy. Trump has not had much coaching on issues, at the minimum, when he should have had a little more depth.
I think what hurt him the most with women, was his tweet of the Pic of Heidi Cruz alongside Melannia. That told women in an unmistakable, no media spin sort of way that Trump values women most for their looks and so many women hate that. Hell, I hate that and I am not a women, lolol. Trump was already down for having a 'foreign Mail Order Bride' thing going and then he compounds it with this; it was just politically suicidal.
Trump needs a political advisor and a second set of eyes to pass EVERYTHING he plans to have in his retort bag and tweet arsenal. Hell *I* could have told him that tweet would cost him about 20% of Republican women voters.