Jonah Goldberg is absolutely right today (I don’t get to say that too often!).
I’m not a binary partisan, but if I were advising the Republican Party, I would tell them it would be foolish to divert any political attention right now from economic issues (such as spending and debt), the growth of government (size and scope), and government failure/corruption. Of course, as a political scientist, I am prone to think the bigger macro variables have the most sway – so a lot of this strategizing and messaging isn’t as important as you might think. But if they are working on the margins, then don’t push pocketbook voters away with social issues from either a conservative or libertarian perspective (unless you can tie them into the larger narrative of government run amok). And I say this as someone who has very strong preferences on social issues and personal freedom issues*
I would guess that Republican party operatives get this. And for what it is worth (n=1, so perhaps not much), I made the case for this position recently to a very well-connected Republican insider, and he agreed.
*(For example, I favor drug legalization even though I think it is immoral to use or abuse most currently illegal drugs).
PILEUS 
Re: your footnote, is it immoral because they’re illegal, or some other reason?
Does your answer extend to medical use, assuming you accept the medicinal properties?
No, I’m with Antigone, morality and law are separable!
I don’t have time right now to give a longer argument, but it boils down to whether the use is consistent with human flourishing. So medicinal use is fine.