Tester has got to be nervous right now with rural trends.
It seems that rural Democrats have mainly recovered in the upper Midwest. But once you leave those borders it gets ugly.
Not saying ND is anything like Montana but Heitkamp's position has only gotten worse.
Montana is actually not that much of a "rural" state, and that is part of the reason why Dems do comparatively well there.
Montana is substantially less "rural" than North Dakota. By that, I mean that the land use in MT is much more oriented towards ranching as opposed to farming (which takes up a greater amount of land with less population, so although ranchers are heavily Republican, you don't get many votes from them), and also a large part of Montana (particularly in the west of MT, which is the more Dem part) is simply uninhabited mountainous wilderness. Montana also has more small cities such as Missoula, Billings, Bozeman, etc than does North Dakota.
This is similarly why Democrats do comparatively well in other states in the Mountain west. Colorado, Nevada, New Mexico, Arizona, etc all have large landmasses, but they are not "rural" in the same sense that, say Nebraska or Missouri outside of St. Louis and KC are rural. That is true to a lesser extent of Montana than of those states, but it still quite significantly differentiates Montana from states and areas that are "rural" further east.