All the things that have gone wrong in this clusterhump of a convention pale before Ted Cruz's non-endorsement. One really can't exaggerate how bad this is for Trump. No politician is more popular with religious conservatives today than Cruz, and he basically gave his followers permission not to vote for Trump. But it's worse than that, because as Marshall points out here Trump's campaign is all about dominance. Again and again he has made conservative alpha males - Roger Ailes, Chris Christie, Paul Ryan, Mitch McConnell, etc. - knuckle under to him, and Cruz just looked him in the eye and kicked dirt on his shoes, right in his own house.
There was a smart way for Trump to handle this, and Newt Gingrich knew what it was: get up and pretend that Cruz said what he was supposed to say. With his reality-distorting skills, Trump might have gotten away with it, too. But it was his own supporters on the floor that made that impossible. Their boos and imprecations made it clear exactly what Cruz was doing.
The only bad news about this is that I predict this will be the best thing that could have happened to Cruz's odious political career in the long run. Right now he might be reviled, but the most likely outcome in November is a Republican party in ruins. They will be desperate for a savior, and it will have to be someone that didn't support to Trump during this election. For the next few elections, I predict that Donald Trump will be to the Republicans what the Iraq War was to the Democrats in 2008. Jeb Bush and John Kasich were smart enough to know this, which is why they stayed home. But Cruz just one-upped them. When he's running for the nomination in 2020 and/or 2024 he will boast about this moment.