Economist/YouGov: Clinton +3 (4-way) / +4 (2-way)

[NOVA Green]

Not sure about the veracity of this poll in particular, but topline numbers seem to match other national polls (Although obviously statewide numbers in places like CA, NY, MA, and TX) could well be impacting national versus swing state polls.

Still, it does indicate that at least nationally, 3rd party and undecided voters will break towards Clinton if forced into a choice in a FTF or heads-up match.