Manchin has pulled away and has it almost locked up, currently Dems are actually more likely to win WV than NV. Polls might change by election day but otoh they might not.
When you consider the fundamentals of the states, it's not like it's a coin flip as to which direction the polls could potentially move toward. Manchin and Heller are clearly more likely to lose ground than gain ground. They're both incumbents with higher name recognition than their opponents running in hostile states (WV much more hostile than NV obviously, but Manchin is far more popular than Heller.)
538's fundamental model actually has Manchin running ahead by 9 points. He's a strong incumbent and he's won big in more difficult environments. The assumption that Manchin is doomed to fall is just an assumption and one that could easily prove to be incorrect. I'm not ruling out the race narrowing but it isn't certain to happen.
