One of the explanations for Trumpmania’s durability is that Trump is basically immune to political attacks. Doesn’t matter what you throw at him — between the cult of personality formed by his hardcore supporters and the outer ring of populists who see voting for him as a way to give Washington the finger, anything you hurl is spitballs off of Superman’s chest.

There’s some truth to that. But what if another explanation for his seeming invulnerability is that there just haven’t been many bullets fired? Here’s one of the most staggering figures you’ll see this year. Remember, this guy has led nearly every poll, in every state, since last summer with 30+ percent of the vote:

The party’s collective shrug over Mr. Trump since he entered the presidential race last summer, and its stubborn unwillingness to treat him as a serious threat, is reflected by the paltry sum that both campaigns and outside groups have devoting to undermining him. In a presidential campaign during which “super PACs” spent $215 million, just $9.2 million, or around 4 percent, was dedicated to attacking Mr. Trump, even as he dominated the polls for months.

Patrick Ruffini puts that in perspective:

Money spent by PACs in opposition to a candidate: Donald Trump 2016: $9.2 million

Newt Gingrich 2012: $22.2 million — Патрик Руффини (@PatrickRuffini) February 22, 2016

Trump, whose nomination threatens to detonate the modern Republican coalition, has faced less than half the attack dollars that Gingrich did four years ago, and that’s in a cycle where Super PACs have spent far more than they did in 2012. How come? One reason is strategic: The primary has been one long game of “Survivor,” with every top-tier candidate convinced that if he can just eliminate the competition and force Trump into a two-man race, the anti-Trumpers within the GOP will unite behind him and propel him to victory. That strategy seems increasingly dubious, but it was Jeb Bush’s plan and later became Ted Cruz’s plan and now it’s essentially Rubio’s plan. If a match race with Trump is the goal, then obviously a lot of the early spending will be aimed at rivals for the anti-Trump slot in the final two rather than at Trump himself. That’s how you end up with Right to Rise dropping many millions on attack ads to blow up Rubio while their attacks on Trump are mostly left to Jeb shouting “Stop being mean to my family!” at the debates.

That’s not the only explanation, though. Some PACs doubtless laid off Trump on the theory that dumping big attack-ad money on him would only hand him more evidence that “the establishment” wants to kill him, which would end up polishing his populist credentials. Arguably it would help him as much as it would hurt. And some big donors, I think, might have held off out of simple fear. Here’s how Trump responded on Twitter today to one of the few mega-rich Republican donors who was willing to bankroll negative ads attacking him. This’ll make a fine entry for my coming daily blog feature, “What If Obama Said It?”

I hear the Rickets family, who own the Chicago Cubs, are secretly spending $'s against me. They better be careful, they have a lot to hide! — Donald J. Trump (@realDonaldTrump) February 22, 2016

Responding to a critic is one thing, threatening them is another. After Trump tweeted that, about a hundred different conservatives in my feed wondered what creative uses President Trump might put the IRS to vis-a-vis his enemies, followed by half of them musing that Trump’s fans would only applaud if he went full Nixon. Regardless, if you’re a wealthy Trump critic, your best-case scenario in paying for ads against him is that his friends in the media will allow him to call in and rip you and your business on air at length as often as he likes. Your worst-case scenario is that you end up on the enemies list of a would-be president who’s not afraid to hold a grudge in office.

Anyway. Now that we’ve reached the final three, Trump is finally going to face withering fire from Rubio and Cruz, right? Wrong:

Kellyanne Conway, president of Keep the Promise I, one of the leading pro-Cruz super PACs, said her group plans to advertise in Arkansas, Georgia, Tennessee and Virginia, with Alabama and Oklahoma also in the mix. The super PAC will air positive ads about Cruz, and its negative ads will focus more on Rubio than on Trump, Conway said. That includes new spots.

Er, okay. But Rubio’s going after Trump hammer-and-tongs, right? Well … no, not really. He criticized Trump politely over foreign policy this weekend, but no one thinks that’s the magic potion that’ll break the Trump spell. Frankly, given Rubio’s Bushian tendencies on intervention abroad, Trump can make more hay with Rubio’s positions on foreign policy than vice versa. Rubio does hit Trump in the new ad posted below, but that message is diluted by the fact that it also hits Cruz — and that’s a risky proposition given that Rubio will need Cruz’s voters even if, against all odds, Cruz drops out of the race before Florida. Even now, with Trump a heavy favorite for the nomination and no time to spare, the two anti-Trumps are still more focused on each other than on the frontrunner. Earlier I said I thought he was an 80 percent favorite to win at this point. Maybe I lowballed him.