By Jon Keller, WBZ-TVBy Jon Keller

BOSTON (CBS) – For the first time in months Republicans have a new front runner for the nomination.

The CBS News/New York Times poll show Ben Carson now in the lead among Republicans nationwide, with Donald Trump slightly behind.

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There are a couple of important points to keep in mind as you digest these poll numbers. First, it’s very hard to poll in a presidential primary or caucus state this far out. Voter exposure to the candidates has been uneven, people are still deep in candidate-shopping mode, and candidates can and do stumble unexpectedly.

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Let’s look at some recent history to show you what I mean:

  • On this date four years ago, pizza magnate Herman Cain was on top of the GOP field, and still had several weeks on top before personal scandal hit and he relinquished the lead to Newt Gingrich, who ran up margins of up to 21 points before being displaced by Mitt Romney in mid-December. Gingrich would return to first place in mid-January after winning the South Carolina primary, and Rick Santorum had a turn atop the polls in February, leading by as much as 15 points before Romney took over for good.
  •  On this date in 2007, Hillary Clinton led then-Senator Barack Obama by 26 points in a national poll. It would be three more months before Obama would take the lead in any major poll, and you may recall that battle dragged on well into the spring.
  • On the Republican side at this point in the 2008 election cycle, Rudy Giuliani held a 15-point lead over John McCain, the eventual nominee. It would be nearly three more months before McCain would finish first in a poll, and Mike Huckabee was in first place as late as January 6th of 2008.
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What’s the moral of the story? Forecasting the future from polls this early is like predicting the World Series winner based in the first few weeks of spring training.

Jon Keller