Cruz had an opportunity to address the ad in his own words. With that opportunity, he fed us the sexist claim that "real men don't attack women," baiting Trump (note that he has attacked Hillary- and not just on policy issues like people have claimed here). Instead of denouncing the ad, he figuratively smiled, claimed he didn't do it, and preemptively insulted Trump's character.
Responsibility is not always so black and white. Cruz had the opportunity to denounce the ad, himself, but he didn't. He is responsible for that.
What some PR expert he hires says on his behalf is not so severely distinguishable from what a super pac says on his behalf. Recall when he fired Rick Tyler ? Did he fire Rick Tyler because Rick Tyler said exactly what Cruz wanted him to say, but he wanted to wash the mud off his own hands ?
Or what ?
I don't think Cruz did or approve the Trump wife ad. There are tons of PR things sent out by various pacs and supporters. The people that run them have a certain discretion. It's reasonable to think that the one who ran the ad would think Cruz would approve, since it wasn't really that bad. They were wrong.
Another reason I don't think Cruz did it is that it invited a reaction against his own wife. I don't think Cruz would tempt fate with his family, though he would with himself. It doesn't make sense. Most things that don't make sense aren't true. IMO.
But the ad with Trump's wife...there really was nothing wrong with it. It wasn't a secret photo. It was out there in the world for all to see, anyway. The ad merely called it to the attention of American voters. If Trump thought his wife was good enough to marry, surely he approved of the work she did before they married. Nothing wrong with the ad. If Trump is ashamed, that's a reflection on him. The pic is a reflection on the wife (the pic makes it clear she'll never be First Lady, though).
Then for Trump to retaliate against Cruz's wife, by implying she's unattractive, is a new low, and it likely cost him the election. That's because he hit a non-politician female with an insult about her appearance, feeding the stereotype of Trump as a misogynistic bully who dislikes women except as arm candy. This is something Trump does regularly.
Trump doesn't get it. First Ladies are not made First Ladies because they're hot. They're made First Ladies because they are one-half of a power couple, and they enable their spouses to become President. They are usually educated, intelligent, classy. Appearance really doesn't come into it. Think Eleanor Roosevelt, one of the greatest First Ladies the country has ever had. Trump doesn't get that he's no longer in television and beauty contests, now.
I think this has cost him the election (if he gets the nomination). His unfavorability rating among women is over 60%. You can't win with numbers like that.