Can we talk about the fact that Johnson's leading Trump among 18-29 year olds?
The right-leaning of the Millennial generation are less religious and have nothing to gain from the GOP's crony capitalism. For them, libertarianism is a new and practically revolutionary ideology. The GOP seems to them a cause for price-fixing, heavy personal debt, and low pay.
The more that Sanders supporters see or hear of Donald Trump, the more realistic they will get about him.
....All in all, margins seem to shrink once one recognizes Gary Johnson as a Third Party nominee who can take a big piece of the vote -- but by doing so he also reduces the threshold for a Clinton victory.