A top tier opponent like Crenshaw could take him down in the primary for sure. He's clearly a long term liability and an underperformer vs. generic R. This latest misstep may not matter by itself, but it's one of many.
Ted Cruz is weird. I don't really know who his base is or how he got his seat in the first place. A senator from Texas? You'd think there would be dozens of top tier candidates for that seat
I can't think of any other guy who has such a national profile yet is despised by nearly everyone, even his own party
He very well may be despised by Republicans on the Hill, but I don't think it really has been sufficiently demonstrated that he is particularly unpopular among rank-and-file Republican voters, despite that being such a prominent narrative. If my recollection serves, his approval ratings were never particularly poor in recent years, and I believe they often eclipsed Cornyn's.
Well, a Yahoo/YouGov poll from about a week ago found Cruz at 24% approve, 49% disapprove. Do with that what you will.