The top chart is the NBC News Poll -- done between August 29th and September 4 of a random national sample of 32,226 registered voters, with a margin of error of 1 point.
The bottom chart is the CNN / ORC Poll -- done between September 1st and 4th of a random national sample of 886 registered voters, and has a margin of error of 3.5 points.
The NBC poll has Clinton with a clear lead of 4 points. The CNN poll has her with a 3 point lead, but that is within the survey's margin of error. And when they considered only "likely" voters, Trump had a 2 point lead (45% to 43%).
So, which poll is right? Personally, I would trust the NBC poll a bit more. First, they have a much larger sample and smaller margin of error. Second, I question the sample that CNN is using. Among the registered voters they questioned were 306 Republicans, 299 Democrats, and 281 Independents. There is simply no way that, among the general public, Republicans outnumber either Democrats or Independents. Survey after survey has shown that the largest group now is Independents, followed by Democrats, and the smallest group is Republicans. That makes the CNN sample very suspect.
There is a big difference between a poll of over 32,000 verses one of less than 1000.
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