Well, there is only roughly 20 miles left to finish the pipeline, about 6% of the overall project.
It is that 6% that has stopped it, like the crossing 90' below the bottom of the now submerged Missouri Riverbed that stopped the Dakota Access Pipeline.
With such projects, every flint flake, every bird nest, every rareish plant, and any cause that can be ginned up to stop completion over the entire length of the line becomes a potential stopper.
While completing the last 20 miles is vital to the success of the project, the other 94%, the permits, right of way negotiations, EIS statements, BLM hoops to jump through (Raptor, 'cultural', rare plant, rare animal, historical significance/archaeological surveys, to name some), etc. are a monumental task. I don't doubt that Manchin had some part in that, and if so should get credit for it because it would be swimming against the current his own Party has generated.
That may not make him some wonderful old guy, but credit if and where it is due.