Mr. Christie and Mr. Rubio are not well positioned to consolidate the conservative opposition to Mr. Bush. They are not necessarily trusted by the conservative grass roots, in part for the same reasons that Mr. Bush isn’t trusted. Mr. Rubio was one of the senators who led the charge for an immigration overhaul in 2013, while Mr. Christie has his own problems on immigration as well as on Obamacare, not to mention his history with President Obama himself. To the extent that either might be acceptable to the right (particularly Mr. Rubio), they lack the credibility to run the type of full-throated conservative campaign that might make them natural candidates for the conservatives…

But if Mr. Bush doesn’t fade quickly, a head-on-challenge from another candidate roughly in the center of the party would be very hard to pull off. It would require an exceptional candidate, one with enough natural appeal among voters to compensate for a disadvantage in the invisible primary, or enough strength in the invisible primary to fight Mr. Bush. Mr. Christie, given his weak favorability ratings, doesn’t look like such a candidate, and Mr. Rubio’s own support collapsed over the last three years even as he received as much or more mainstream news media attention as any other candidate.

We’ll probably get a sense for whether Mr. Rubio and Mr. Christie are stronger than they now appear — or whether Mr. Bush is weaker — over the next couple of weeks.