Trump chose to escalate situation by leaking news to friendly delegations & instructing them to boo
In fact, in response to the news that Cruz was going to make a speech that did not explicitly endorse him, Trump intentionally chose to escalate the situation by leaking the news to friendly delegations and instructing them to boo Cruz to make this a bigger deal that it otherwise would have been. If Trumps delegates had not booed and caused a ruckus, but instead had remained silent or applauded at Cruzs exhortation to vote for down ticket races, everyone today would be talking about Pence and his speech, and the discussion would be about positive things associated with Trump and Pence and how they are going to move forward after the convention to at least possible victory.
But that is not what Trumps supporters are interested in. They are interested in having a constant object of hatred and scorn, and its preferred if the target is a Republican. This is the driving force behind their support for Trump, principles be damned. Trump knows it too, which is why he was perfectly happy to let Ted Cruz go on stage, as long as the signal was clearly sent to his supporters that Ted Cruz is supposed to be the new object of hate.
(from Redstate even)
http://www.redstate.com/leon_h_wolf/2016/07/21/ted-cruz-really-proved-last-night/