Why not? After all, Republican party actors remain sharply split over him. A small number of movement conservatives consider him a hero, and his presidential run drew considerable support from Republican state legislators and from some party-aligned interest groups. But most everybody else -- especially those who have worked with him in Washington -- still appear vehemently opposed to him.
Some Republicans may really believe Cruz's defiant "vote your conscience" stance at the convention in Cleveland will matter to Texas voters almost two years from now, and enough so to make them vote against him. Mostly, the Republicans are just using his speech, which they saw as grandstanding, as an excuse to organize against him.
Recall that in the weeks leading up to the Iowa caucuses - when Cruz and Trump were running even in the polls - a number of high-profile Republicans suddenly softened on Trump, and in several cases even said they preferred him to the Texas senator.
Many Republican National Committee members might have been terrified that Cruz would wind up as the presidential candidate if the Dump Trumpers had succeeded in freeing the delegates at the convention.
But now we're not talking about national politics. We're talking about Texas. The Cruz faction is much larger than the opposing GOP forces in the state. In 2012, Cruz, a political novice, defeated the heavily favored Republican lieutenant governor, David Dewhurst, by outflanking him on the right. And Cruz easily defeated Trump in the Texas presidential primary.
The common thread in Texas is that the candidate accepted as the most conservative wins. In 2010, Rick Perry, who though he was governor never had strong approval numbers, easily clobbered the more mainstream conservative Kay Bailey Hutchison when the veteran senator challenged him in the primary.
It's possible Trump will try to take vengeance on those he perceives to have undermined him, but it seems unlikely a candidate who barely has the ability to run ads for his own presidential effort will do so for a Cruz challenger two years from now.
If Trump loses, we have no idea what the Republican Party will look like. Perhaps a few of the Republicans from all factions will embark on the hard work of fixing what's wrong with the party. But they are unlikely to be a majority. Most will simply blame other party factions and try to forget the whole nightmare of 2016. So, for example, members of the House Freedom Caucus and other radical conservatives may say the loss resulted from having too moderate a nominee, just as they did after John McCain and Mitt Romney lost.
And in the event Trump wins? Then the Republican Party would be governed by his whims, which are largely unpredictable. And Ted Cruz will be the least of their problems.