"Ted Cruz, counting on a Trump defeat in November, has positioned himself as a principled holdout, apparently convinced that refusing to endorse his party's presidential nominee will boost his 2020 stock among Republican voters, who will realize they nominated the wrong candidate this time around."
Cruz is refusing to endorse Trump on principle. I don't know how much clearer this could be.
This writer, on the other hand, is the one with the agenda. He hopes to paint Cruz as a crass opportunist so it can be used against him at the next national election.