I can believe it if all those undecided republicans come home and he loses 90% of the undecideds.
I hope not, but wouldn't be surprised. It always seems like when Democrats are narrowly leading in red state gubernatorial races, all the undecideds break for the GOP at the last minute (KY-2015, KS-2014, MO-2016, IN-2016, SD-2018, OH-2018), but the opposite never really happens in blue state gubernatorial races where Republicans have small leads going into election day (VT-2016, MA-2014). Hell, they even win races sometimes when they are polling behind! (MD-2014, IL-2014)