WILL BEN CARSON BE THE ONE PERSON TRUMP CAN'T ATTACK?

There's yet another Iowa poll with Donald Trump and Ben Carson at the top -- but in this one they're tied:

Ben Carson and Donald Trump are tied at the top of the Republican field in a new survey of likely Iowa caucus-goers with 23 percent each, according to the results of a Monmouth University poll released Monday.

The good news continues for the retired neurosurgeon with his favorability ratings, as 81 percent said they view him favorably, compared to just 6 percent who do not....

Carson leads among Evangelical voters, earning 29 percent to Trump's 23 percent, while non-Evangelicals backed Trump with 24 percent, followed by Carson at 18 percent and Fiorina at 13 percent.

Here are the rankings -- which are quite ugly for Jeb Bush, as well as for former Evangelical favorite Mike Huckabee:

When Iowa Republicans are asked who they would support in their local caucus, Ben Carson (23%) and Donald Trump (23%) tie for the top spot. The next tier of candidates includes Carly Fiorina (10%) and Ted Cruz (9%), followed by Scott Walker (7%), Jeb Bush (5%), John Kasich (4%), Marco Rubio (4%), and Rand Paul (3%). The last two Iowa caucus victors, Mike Huckabee and Rick Santorum, each garner 2% of the vote. None of the other six candidates included in the poll register more than 1% support.

So there may be a limit to Trump's dominance of the polls. Now, what does Trump do when he feels challenged? He lashes out in a crude and nasty way. So far, he's gotten away with every attack -- on John McCain, on Megyn Kelly, and so on. He's certainly not upsetting anyone by attacking Jeb Bush and other Republican candidates. It seems as if he can get away with attacking anyone.

Now that Carson is threatening to take the lead from Trump, isn't Trump going to attack Carson, crudely and nastily? And what happens then?

I know that Republicans are awfully comfortable with racism -- send them an email forward with a bone Photoshopped through Obama's nose and they'll send it to ten more friends with the subject line HILARIOUS.

But they're awfully protective of black conservatives. They love Clarence Thomas and Allen West and Thomas Sowell and Mia Love. And Carson, although he severely criticized President Obama in that National Prayer Breakfast speech, is usually not in attack mode. He has a nice-guy image. My sense is that conservatives regard him as, well, saintly.

True, they didn't rally around Herman Cain four years ago. But it seemed clear that Cain was guilty of the behavior of which he was accused -- the National Restaurant Association, of which he was chief executive, paid money to one woman who accused him of harassment. and he acknowledged making payments to a woman who said she'd had a long extramarital affair with him.

Trump will probably attack Carson without provocation. He'll say Carson is "weak." He'll mock Carson's way of speaking or something Crson said. He'll say he's known some of the world's top surgeons -- brilliant doctors, he'll say, but otherwise they're not very bright. That's what Trump does.

I know that the safe bet is that Trump will get away with everything, but I'm not sure he'll get away with this. Too many white conservatives really like themselves for liking Carson. They wield their admiration for him as proof that they're not racist, no matter how many nasty things they say about Al Sharpton and the Obamas and Black Lives Matter. Trump's Teflon will probably hold, but Carson just might be Trump's nemesis.