The poll is of registered GOP voters, not likely voters which is important when comparing polls by different organizations. The Rasmussen poll discussed last week which among other things reported a drop in Trump support was of likely voters.
Ted Cruz's results are particularly surprising, because the initial reaction was he had a good debate.
Note in the chart below the candidates who are outside of the top ten (Like Fox News, CNN's debate on 9/16 will split into two groups top ten and bottom seven). George Pataki and Jim Gilmore did not generate enough interest to register in the CNN poll (perhaps it's time for them to say goodbye).