Why is the race tightening?

[Coolface Sock #42069]

Clinton's support goes up and down, but Trump's had a hard ceiling so far that he's yet to really break through. I doubt he's getting a lot of undecideds when November comes around.

But Clinton losing support seems to be the main reason it's tightened.

Also, the media is going to try to further tear Hillary down so they can have their "horse race". I'd expect this in any election from here on out in which there is a clear frontrunner.