So far, Trump’s rivals have mostly left him alone for tactical reasons, but they may soon unleash their attacks.

The media are mystified. The partisans are flummoxed. Eight months into Trumpmania, the Donald’s popularity has shown no sign of abating. He just breezed to a 20-point victory in New Hampshire, and he now commands an unambiguous (if very early) lead in the delegate count. So why has no one bothered to mount a sustained attack on the GOP front-runner? As of late January, “literally, zero dollars in super PAC advertising [had] been run against him,” said the Washington Examiner’s David Drucker. The overwhelming majority of the fire from all sides has been directed farther down the polling ranks at Marco Rubio, who has absorbed tens of millions in negative advertising in recent months. The casual observer could be forgiven for thinking the candidates had all gone mad.

Yet however reckless this one-way ceasefire might be in the aggregate, it is brutally rational from the standpoint of the individual campaigns. It’s not that the other Republicans have deemed Trump invincible, that they’re scared of blowback, or that they’re pulling punches. Every campaign has a strategy to deal with Trump. Every apparatus has potent attacks at the ready. Every candidate is itching for his shot. The problem is the way the incentives line up. As Jay Cost has phrased it, the motives have yet to align with the means. Plenty of outside groups have altruistic goals of saving the party and the broader conservative movement from Trumpism, but they have not found the right patrons to finance their efforts. The campaigns, and particularly their allied super PACs, have ample means, but no motive at this juncture.