July 19th – over three months ago. That’s the day that Donald Trump took the lead in the RCP average of polls for the Republican nomination. Since that time, he has not been seriously challenged for the lead by anyone, until now. Against all odds, the first person to actually threaten Trump’s position in the GOP catbird seat is Ben Carson.

Eventually, I find it likely that someone like [mc_name name=’Sen. Ted Cruz (R-TX)’ chamber=’senate’ mcid=’C001098′ ] or [mc_name name=’Sen. Marco Rubio (R-FL)’ chamber=’senate’ mcid=’R000595′ ] or Carly Fiorina will be the last man (or woman) standing for the GOP nomination. But for now, those three (along with the other also-rans like Jeb Bush and Chris Christie) have floundered and flailed away at Trump’s standing, to utterly no avail. They have tried attacking him directly (Bush), ingratiating themselves to him (Cruz), or largely ignoring him (Rubio) and yet they have all only cracked single digits in the polls fitfully. Only Carson has been able to deliver an actual dent in Trump’s seemingly impregnable base of support – at least, for now.

This will create a fascinating dynamic in tonight’s CNBC debate. Until now, the other candidates have mostly ignored Ben Carson. Carson is a candidate that they have not dared to attack, even more than Trump. Whatever Republican voters think about Carson’s policies (to the extent that he has them), or his readiness to be President, they almost all uniformly find him “nice” and “likeable.” Up until this point, no one has figured out how to mount an attack on Ben Carson without risking being perceived as a jerk and alienating his growing bloc of voters.

The million dollar question about tonight is: will that continue? Will the other candidates continue to allow Carson to emerge basically unscathed in the hopes that Carson will continue to just eat away at Trump’s base of support, or will someone be desperate enough to take a swipe directly at Carson?

I will tell you one candidate who will definitely have Carson in his crosshairs: Donald Trump. Carson should be prepared for Trump’s unique brand of, uh, criticism, which might well include sideways (or direct) attacks on unexpected subjects – like, for instance, Carson’s religion. Trump has already begun his attacks on Carson on the stump, accusing him (with almost hilarious hypocrisy) of being a recent flip flopper on abortion.

Trump, though, will be fairly easy for Carson to laugh off with an easy shrug. “I’m not going to engage that” is a relatively easy response to Trump’s borderline insane flim-flammery, and is moreover a response that’s right in Carson’s rhetorical wheelhouse.

But what happens when and if Carly Fiorina points out that he doesn’t exactly have a tax plan, or [mc_name name=’Sen. Ted Cruz (R-TX)’ chamber=’senate’ mcid=’C001098′ ] presses him on what he would use budget reconciliation for, or [mc_name name=’Sen. Marco Rubio (R-FL)’ chamber=’senate’ mcid=’R000595′ ] poses a tough question to him about Cuba? In the second debate, when Carson was asked even mild questions by the moderators, he was able to deflect with “I don’t know” type answers because none of the candidates on stage had a vested interest in attacking him.

Tonight, Carson is likely to face tougher, more hackish questions from the most aggressively liberal moderator the candidates are likely to face in this debate cycle. His supporters will rightly criticize many of the questions he is likely to face from the moderator (and perhaps from the other candidates) as unfair, but his ability to handle these questions will presage how he is likely to handle them from an increasingly hostile media in the general election.

For the first time this debate season, Ben Carson enters the debate stage as the candidate with the most to prove, and the most to lose. Will he rise to the pressure or will it crush him? We’ll find out by this time tomorrow.