I suspect that is due to the density of the population around Helena and Missoula (UofM). This is far too endemic of the Electoral College. Unless it is changed to attenuate the effect of population centers, this Nation is not long for this Earth.
Montana is an old railroad/mining/union state, and in fact is a closed shop state.
Like the Dakotas it also has large numbers of old folks, farmers and Indians who, like it or not, have been conditioned to look to the government for sustenance.
In addition the wealthy lefties who have already ruined Colorado, to name one state, are also moving to Montana in large numbers.
Still Daines is a decent fellow, good-natured and apparently squeaky clean and, as per Viennacon above, if he doesn’t fall on his face it seems he’s on track to win.
The state is heavily dependent on the Fed's to provide highway funds, farm subsidies, student loans, military pay and pensions, federal retirement, Veterans benefits and Social Security.
Anybody wanting to get elected Senator here has to guarantee Montana voters that none of those programs will be cut....