Yes, it will work if Trump is the GOP nom.
Manchin will pull votes away from the Trump if he's the GOP nom and hand the election to the Dem (unlikely Biden, just my guess.)
Manchin will pull votes away from the Trump if he's the GOP nom and hand the election to the DemOnly from the (you?) slack-jawed knuckle draggers at FreeRepublic that were braying for Manchin to switch parties.