Republican Presidential Debate

Is the long awaited Trump fade finally here?

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Two polls this week found Donald Trump trailing Ben Carson in Iowa, site of the first contest in the 2016 race. The second survey, out Friday, showed Carson with a solid 9-point lead, 28 percent to 19 percent, over Trump. An earlier Quinnipiac poll showed Carson leading Trump in Iowa by 8 points.

In typical style, the braggadocious billionaire dismissed the results of the Quinnipiac poll in interviews and on Twitter, where he retweeted a supporter's comments saying "#BenCarson is now leading in the #polls in #Iowa. Too much #Monsanto in the #corn creates issues in the brain?"

Donald Trump (L) and George W. Bush (R).
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Trump later deleted the Tweet and blamed it on an intern: "The young intern who accidentally did a Retweet apologizes." This columnist was always under the impression that Trump did his own tweeting. But apparently that is not so.

Whatever the case, Trump will now have a hard time disputing two polls showing almost identical results in Iowa. His lead there, it would appear, is gone.

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This setback in Iowa raises the critical question about the Trump candidacy: Will his outsized ego and distaste for failure allow him to stay in the race if he is no longer the dominant front-runner? Of course, Trump still leads in national surveys, but his lead over Carson is now just six points. And national surveys this early in a presidential race are of little real value. They tend to reflect media coverage (of which Trump has had an unlimited supply) rather than real voter scrutiny of the candidates.

Polls that measure what GOP voters are actually thinking in the early states — like Iowa — are much more significant. And they are starting to show Trump slipping, though he maintains a big advantage in the first-in-the-nation primary state of New Hampshire, where evangelical voters are less of a factor.

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Trump's Iowa slippage reflects what the rest of the field has long thought would be the shape of the race: an eventual Trump fade that returns the campaign to a more traditional footing. This theory of the case, shared by Jeb Bush and Marco Rubio backers, holds that once voters focus on who might actually win, protest candidates like Trump (and eventually Carson) will fall by the wayside and more establishment-friendly candidates will rise to the top.

Bush has repeatedly said he is playing the long game and will have the resources and infrastructure to begin piling up delegates as the race goes national in the weeks after Iowa and New Hampshire.

Predicting an end to the stunning rise of Trump has been a fool's game. And it may prove so again. After all, the billionaire is still slated to host "Saturday Night Live" next month and could get another wave of national support. But it's worth considering who might gain the most from an eventual Trump exit.

One obvious possibility is Carson. But other campaigns, including Bush's, have their eyes on Ted Cruz.

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The senator from Texas has assiduously defended Trump during the campaign and made a fairly obvious play to be the recipient of The Donald's supporters should the time come. And Cruz had nearly $14 million in the bank at the end of the last quarter. One Bush fundraiser told me this week: "At first I thought the angry, frustrated vote would coalesce around Cruz or Rand Paul. … Instead it coalesced around Trump. Now we've seen Ben Carson and Carly Fiorina get a look. But if Trump does implode, a lot of his support could easily shift to Cruz. He has a ton of cash on hand. He is in a very, very good position to make a move. Marco is kind of like Jeb-lite."

Despite this offhanded dis of Rubio, the senator from Florida remains a candidate to be watched closely should Trump and Carson fade. Rubio and Cruz are essentially deadlocked for third in the latest Iowa poll. And Rubio has also been running a lean campaign and retains around the same $10 million cash on hand as Bush.

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The former Florida governor does have the advantage of having nearly $100 million in his Right to Rise Super PAC. But it costs much more for super PACs to run ads than hard money campaign committees, so the advantage is not as large as it appears.

It's far too soon to declare two Iowa polls as the end of Trump's poll dominance. But it could be the end of the beginning. And if the slide continues, Trump could do what he's done in the past when deals go south: get out fast and save himself from embarrassment.

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— Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money []. Follow him on Twitter @morningmoneyben.

Watch CNBC's "Your Money, Your Vote: The Republican Presidential Debate" on Wednesday, October 28. The debate will feature two sets of candidates discussing critical issues facing America today, including job growth, taxes and the health of our economy. Coverage begins at 5pm E.T.