Like you, I think Colorado is the reason. Trump rightly viewed that situation as one the American people would turn their noses up at, and he was right.
I don't think the race will turn back again. A solid trouncing in New York tomorrow, big wins in other Eastern states, rising poll numbers in California... it's over.
I think it's over with pledged delegates before the Convention, and for sure it's over on the first ballot anyway. Manafort is closing the deal with uncommitted delegates daily.
Just goes to show - Cruz may be smarter at lawyerin' up the rules, but Trump is smarter at actually figuring out people.