Stewart prevailed in the 9th Circuit - just one step below SCOTUS - going so far as to affirm that a convicted felon could make and own home-made machineguns, based solidly on the 2nd Amendment. The case was appealed to SCOTUS, which without discussion remanded the case for review in light of Raich (note that SCOTUS did not reverse Stewart, it just said Raich had to be taken into account).
Raich ruled that any action reducing demand in an illegal interstate market fit application of the Commerce Clause. This, of course, is absurd and must be revisited - what better revisiting than a state demanding independence of intra-state activity exercising a Constitutionally-protected right? Presumably Montana, as a state, can argue better and with more weight than a terminally ill grandmother growing a half-dozen plants for personal use.
Understanding these cases is indeed important. Doing so facilitates understanding the way to success; doing so does/should NOT be grounds for giving up.
I believe part of the Montana bill states that Montana will defend whoever is arrested/fined/whatever by the feds.