I'm pretty sure he'll win in 2018 unless Trump goes nuts.
As a Marylander do you know why his approval rating is insanely high? I know he's known as a centrists and non-ideologue but it's hard to fathom that kind of approval in today's polarized American.
EDIT:
Doing more research. Apparently he's responsible for ending the Baltimore race riots by bringing in the national guard. He also brought Maryland's debt from 5.1B to 600M through fiscal restraint. He's respected for being non-ideological, and on top of that he was diagnosed with Leukemia and battled through it in 2015.
Really, he hasn't done anything to piss people off. I am as liberal as they come, but if I was polled I would say I approve. I won't vote for him in 2018, but I wouldn't be crushed if he won again.