If we assume (and we do) that Cruz was motivated in part by the thought of running for president again in four years, he basically signaled that he plans to climb the ladder of power again exactly as he did these past few years.
In his speech, Cruz noted that “citizens are furious—rightly furious—at a political establishment that cynically breaks its promises and ignores the will of the people.” When the crowd erupted in anger at him, he paused to relish it, as if to say, “You are unanimous in your hatred for me, and I welcome your hatred.”
What has changed since he was a presidential primary candidate trying to win over Trump supporters is that they have become the political establishment. Cruz spent 2012 through 2015 converting establishment hatred into political power. With Trump as the new establishment, he’s signing up to do it again.