As a side note, the poll was done over 3 weeks rather than the traditional shorter time. So I don't know how trustworthy it is. This goes the same for the UT-04 poll, the gubernatorial poll, and the Senate poll, all of which were asked in this same large poll.
Also apparently a lot of the undecideds told Dan Jones that they wanted to just write-in Mitt Romney. I'll have to dig up the tweet where Dan Jones or another pollster mentioned that, but if true, that McMullin guy will have a fun time here.
Today on MTP Daily Steve Kornacki said they told him 14% volunteered they would write in Romney. A Romney endorsement of Johnson or McMullin would be a big deal in UT and certainly make it interesting. Without UT, Trump would need to win FL/OH/PA and one other state (probably IA).