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.
Yep, the Kalifornicators are infesting Missoula, Bozeman, and likely Butte.
Actually Montana is more of an agriculture state. The enviro-weenies have pretty much killed the mining industry around western Montana. There's still some mining, but it's nothing like it was 40 or 50 years ago. The railroads don't stop in Montana, they go right through it. Eastern Montana is seeing some benefit from the oil industry in North Dakota.