Assuming these statistics are somewhat accurate (even if they're not, I think various groups tracking with one another could still be)...
Stereotype the average Romney '12-Dem '18 voter and the average Obama '12-GOP '18 voter. The parties have traded millions of these voters with one another over the time period. On one hand, you have a disproportionate NIMBY, family values-type cohort with conservative worldviews on behavior versus a loud and rowdy white trash constituency that has never exactly been socially statist when it comes to what people do with their bodies.
I don't necessarily see my preferred choice as an option in the poll. I could totally see these people being below 50% support (or even on par with the GOP at-large) when it comes to legalization. I imagine they're considerably less supportive than Democrats at-large (but more so than the GOP) on decriminalization, but comparable to Democrats on medical use.
So basically: definitely OK with medical, probably OK with decriminalizing and not OK with legalizing (options 2 or 3 depending on how you read it - voted option 3).