To give actual advice, They must keep playing the moderate card. Liberal candidates won't make the cut so the Democrat has to be moderate.
Joe Manchin's dw-nominate score:
-0.069
Robert Byrd's dw-nominate score:
-0.298
Greater negative scores indicate a Senator being more liberal. So it seems that Byrd was more liberal than Manchin. It would almost seem like the fact that Democrats once used to run a monopoly in West Virginia had nothing to do with ideology but with identity.
It would almost seem like, and hear me out here, WV circa 2020 may be a wee bit different from WV circa 2006. A Democrat who doesn’t cultivate a moderate cozy-up-to-Trump persona will lose by double digits because enough of West Virginia has drunk the Trump Kool-Aid to reflexively vote them out. Manchin does not have the same freedom to be liberal that Byrd had in 2006.
If Byrd were running in 2018 and had voted against Kavanaugh he would have lost. Manchin made this calculation and survived.