Why is Heitkamp so vulnerable...

[Person Man]

It maybe because large numbers of residents of North Dakota understand that a Democrat majority Senate would do everything it could to shut down North Dakota’s fossil fuel energy development.  They also understand that would include the shutting down of the appointment of individuals who support fossil fuel development. And Heitkamp would likely have no ability too change these actions.

That wouldn't explain why the Dakotas were so democratic friendly pre-Obama downballot.

Democrats didn't start to become overtly hostile to coal and fossil fuel energy until Gore 2000.  Obama 2008 was when the feelings truly manifested themselves, though, and the Dems have been on a downward spiral in oil and coal states ever since.

So it's quite simple. Big Oil.

Then again, how is Manchin hanging on?

[Person Man]

The only way to be competitive in enough states to be competitive in the Senate appears to either drop the Environment as an issue or to finally break the energy cartels power over these regions through research, development, and policy.