The unfortunate demographic is that three cities (Grand Forks, Fargo, and Bismarck) have about half the voters, and none of these have any oil under them.
The rural areas in the west which have oil have been growing, infrastructure funding has been spent to keep roads which have incredibly heavy truck traffic passable 'out west', and Fargo has lost it's prima donna status.
Before, flooding along the Red River has kept the money rolling in, along with the colleges in Fargo and Moorehead and the Air Base in Grand Forks. Note that while Fargo and Grand Forks are served by I-29, Fargo and Bismarck by I-94, the highways leading to the oilfields are of lesser construction, and US 2 was only recently made into a 4-lane highway. Highway 85, the major N/S highway in the region got some passing lanes last year, but is primarily only a two-lane highway, so some money has been spent upgrading these and myriad other roads which have been subjected to a large amount of heavy truck traffic.
With the economic input of the oil producing counties, the balance of power is shifting in the state, from east to west. The response from the Fargo Forum newspaper and others (especially Democrats in non-oil producing counties) has been that the West's newfound prosperity is somehow evil, and measures should be taken to slow that growth down.
While that prosperity has indeed produced growing pains with challenged services and infrastructure, housing shortages, and higher prices, it has also brought with it the sort of economic development which many politicians talk of and few deliver (as if the market did not deliver--they were mainly along for the ride, and decided to go with the flow rather than buck the tide).
Wages are high, the unemployment in the Western part of the state is low (1.8% in Williams County), and business is flourishing despite high rents and housing prices. The shortage of housing is being met by the private sector (if you come, they will build it), and as growth rates slow, that part of the economic picture is approaching equilibrium. Rents will fall as that gets more competitive, and all but high end housing prices will moderate.
I think RCP has greatly exaggerated the popularity of Heitkamp, and this smells of the sort of tactics designed to demoralize opponents.
I am one more that has noticed RCP has gone to the Dark Side since 2010.