CNN poll was taken mostly before the debate, and has a small sample on the one day after the debate. ARG has a MOE of 5 points also, so Cruz could be as high as 19, which would be in line with the other poll showing Cruz and Rubio tied post-debate. ARG was pretty close with Trump in New Hampshire, and one point off on Cruz's numbers, though their last poll I think was either just before or not long after the debate, so they were wrong with Rubio.
Good thing for Trump that CNN poll only had one day after the debate, or the results would have been a lot worse for him. According to the internals, Trump was running at 40% before the debate - he dropped to 31 % the day after.