Manchin was was governor when I lived there and he's rather popular. It wouldn't be a landslide but he'd beat either of the 2 milk toast Repubs not in a landslide but pretty handily. He's triangulated so much that there really isn't anything they can attack him on.
Blankenship will have 6 months to unleash the racism while convicing his voters that Killary was responsible for those miners deaths, Obummer regulations turned Parkersburg into cancerville USA, and the Elk River spill was a secret EPA plot. There is enough dumb and oxycodone riddled voters in that state to push him over the top in a general election. He'll have full support from the RNC. Don't forget, Moore got 49% of the vote and only lost because of big time turnout from blacks, not something that WV has much of. Pay no attn to the polls Trumpists think the media is the deep state and wouldn't talk to them anyway.