I have been a huge supporter of Cruz's and I am thoroughly disappointed. IMHO... something or more likely someone got to Ted. I question what is truly going on ... the timing for one seems a bit odd to me. I would have thought if he were going to announce he was going to vote for him, he would have done so closer to the election instead of a month out and certainly, I would think he would have waited till after the first debate. IMHO Ted has made a huge mistake ... there is a strong possibility that Donny could make a total asz out of himself during the debate and even more likely that he will display his lack of knowledge on the issues, government and the Constitution.
On the other hand Since Cruz has fought several Supreme Court battles (Heller v. DC etc.) and won, I think Scalia's vacancy may have weighed heavily on him and the fact that at least one other additional justice will probably be appointed. Cruz stated; "We know, without a doubt, that every Clinton appointee would be a left-wing ideologue. Trump, in contrast, has promised to appoint justices 'in the mold of Scalia'".
Cruz unfortunately, is taking him at his word.
..."Cruz also praised Trump for releasing an updated list of potential Supreme Court nominees that includes Sen. Mike Lee. Cruz said he had sought "greater specificity on this issue, and today the Trump campaign provided that."
http://www.foxnews.com/politics/2016/09/23/cruz-says-will-vote-for-trump.html