Normally, I'd dismiss such a decline as statistical noise and want to see other polls before declaring that the President's standing among the public has diminished.
Government and public administration
Political Figures - US
Here's the thing: CNN's poll is only the latest in a series of high-quality, live-interview polling over the last two weeks to show that Trump's approval rating is down. This dip could have a major impact on the midterms if it holds.
Eight high-quality polls have been completed over the two last weeks -- and every single one of them has Trump's approval falling.
In the latest average, Trump's approval rating is about 38% in eight polls from ABC News/Washington Post, CNN, Gallup, IBD/TIPP, the Kaiser Family Foundation, Quinnipiac University, Selzer & Co. and Suffolk University.
If we just took an average of the last polls by these organizations completed August 27 or earlier, Trump's approval rating stood at 41%.
Now, not all of these pollsters show the same drop. Trump's 6-point decline in CNN's poll is the largest. When you take an average of their latest two tracking polls compared with their prior two, Gallup has Trump dipping just a percentage point.
You'd expect such differences though given sampling error.
An average 3-point decline is rather remarkable for a President whose approval rating has been one of the steadiest on record. It would suggest that something the President did had a real impact on public perception.
House Republicans should worry about Trump's approval rating drop, if it holds through November. Voter opinions of the president have been increasingly tied up with how they vote in midterm elections.
CNN polling has regularly found that more than 80% of voters who approve of Trump are voting for Republican House candidates, compared with more than 80% of voters who disapprove of Trump voting for Democratic House candidates.
For Republicans to have a realistic (i.e. within the margin of error) shot of maintaining control of the House in 2018, Trump's approval rating must remain at least in the low 40s nationally.
For them to have a 50% chance of holding on to power in the House, Trump's approval rating will likely need to rise into the mid-40s.
Right now, Trump and his fellow Republicans are ... going the other (i.e. wrong) way.