That's because Trump has made himself radioactive.
If Trump had disappeared from the American political scene after his big win in Arizona, he'd have wrapped up the nomination by now. Instead, he defended his lying campaign manager, Corey Lewandowski, after Lewandowski was charged with battery for allegedly grabbing, yanking and bruising a reporter; tweeted nastily about Heidi Cruz's looks; repeatedly suggested that Cruz had violated federal law without evidence; trotted out surrogates to slander anti-Trump women as Cruz's adulteresses; flipped his abortion position four times in less than three days; found himself on the short end of the interview stick with a Wisconsin radio host; labeled health care, housing and education as key functions of the federal government; accused the Republican National Committee and state delegations of attempting to "steal" the nomination from him by engaging in traditional delegate politics; and stated that he would likely select Supreme Court justices who would investigate Hillary Clinton's email server, for starters.
The more Trump talks, the worse he sounds.
Now, Trump's supporters keep saying he's just learning the ropes. After all, he's never run for political office before, so a few hiccups are to be expected. But Trump continues to demonstrate a complete inability to learn. After losing Wisconsin, did Trump turn down his "Spinal Tap" speakers from volume 11 to 8? Of course not. He turned the volume up to 12 with a campaign statement that bragged that Trump's 13-point blowout at Cruz's hands was actually a big win in which he "withstood the onslaught of the establishment yet again." The statement also stated openly, and without evidence, that Cruz had illegally coordinated with his super PACs, and slammed Cruz as being "worse than a puppet -- he is a Trojan horse, being used by the party bosses attempting to steal the nomination from Mr. Trump."
Trump's campaign is flailing because it's not a campaign; it's a self-produced vanity reality TV special. Trump didn't bother to learn the delegate rules because he couldn't be bothered to do so. He doesn't bother to learn the ins and outs of his own policies because, hey, why bother when people flock to you for shouting slogans about building walls? Last month, he fired his data team manager and elevated the second in command. But the second in command apparently doesn't know politics, or even how to access the data itself.
But don't worry: Trump has a very good brain and hires all the best people.
By the time of the Republican National Convention, Trump will be 70-years-old. Sadly, he has significantly less self-control than my 2-year-old daughter. He's spent his entire life being handed things: money, fame, female companionship. Now he can't understand why he's not being handed the nomination. So, like Veruca Salt in "Willy Wonka and the Chocolate Factory," he'll scream.
It won't work. Trump joked months ago that his strategy was to "keep whining and whining until I win." But now he's beginning to lose. And the whining won't stop anytime soon.