Seriously. You primary him and you'll lose 100%. Not saying he'll win, but moving to the left only decreases your odds. You don't want to pull a Tea Party and reduce your odds in key races.The fact that even Donnelly and Heitkamp voted against Sessions (along with all Dems other than Manchin) is kind of impressive.
I know a lot of people want to primary Manchin, but I'm not sure if you can win as a non-racist in West Virginia. The state is sad.