Seriously, what is going on at this Republican debate?

Tonight was supposed to be the last stand of John Kasich and Marco Rubio. Tonight was supposed to be an extension of the last Republican debate, the most vulgar presidential debate since the 19th century (probably). Tonight was supposed to be a bloodbath! 

Instead, this debate has been civil. Trump has typically set the tone of these debates, and tonight he’s largely refusing to engage, even when provoked. What’s surprising, though, is how little provocation there is: Kasich and Rubio have every incentive to set off some fireworks, but they’ve acted like they were frontrunners, not left for dead in their respective home states. Donald Trump even praised the debate for being so civil! 

Here is the first attack of the debate, which is arguably Trump’s weakest burn of the entire campaign. 

So what’s going on? Has Trump decided that dragging the debate into the gutter will hurt his very transparent pivot toward the general election? Did the candidates agree beforehand to be civil to each other? Are they wearing weird collars that shock them if they say mean things about each other? Or has Donald Trump decided that it’s just not worth it to insult his opponents anymore?