I think an apology would go a long way. It doesn't have to make him look weak. But let's be real - he campaigned like an butthole. Cruz treated him cordially, and then Trump pounced, insulting his wife, besmirching his honesty, and, on the eve of closing the deal, spewed tabloid rumors about Cruz's dad being involved in the JFK killing.
Now Cruz was supported by a whole lot of folks, good Republican folks, who rightly admired the guy, so how the hell are they supposed to turn around and support Cruz after he's so personally insulted their candidate, and by transference themselves? This was deliberate character assassination so Trump could jazz up his mob. He took out most of the other candidates the same way, with deeply personal insults. The fact that he convinced a plurality of voters to admire his tinpot crapola is astonishing, but not more so than the Trumpsters' demands that we now all kiss up and make nice. For who? For what? Trump will stick a shiv in you if your aren't looking. We all know who this man is, and who (some) of his followers are.
Yeah, an apology would be a real wise thing.