That's an interesting observation that I have also made in the past. You can easily draw that conclusion by simply looking at the Real Clear Politics average of Trump vs. Clinton over time. Every time the RCP poll average shows Trump closing the gap we get a flurry of pro-Clinton polls.
Take a look at the RCP chart below and you will see what I mean. Trump has reached a tie with Hillary 4 times and is heading toward a 5th. Watch for the Hillary "bounce" very soon.
