> Do I have this right: your State says your medicine is legal to buy, the Federal government says it's not illegal

No, the second half is wrong; the Feds say it is absolutely illegal, but also not a prosecution priority. Well, except the “not a prosecution priority” part just got a little less clear.

As far as I understand, your state says it’s legal but the federal government says it’s illegal. However, there’s a standing directive from the Justice department that they won’t prosecute individuals complying with state laws (when those state laws legalize marijuana).

So it’s still illegal at a federal level, but the department that would ostensibly enforce that simply let it be known that they would defer to state law and not prosecute when state law legalized it.

But since it was never actually legalized at the federal level, it’s little more than a gentleman’s agreement (which could be pointed to as a valid defense if someone was prosecuted federally). But since the directive came from the executive branch, it can also revoke/revise that directive as it wants, and begin enforcing those federal laws regardless of state level legalization. Congress still has the power to pass actual laws that decriminalize it federally, but they’ve conveniently been spared from that politically charged topic by the Justice Department directive. Now they’ll be forced to address it. And with hundreds of millions of dollars in state tax revenue at stake, there will likely be more pressure to not white wash over it than their has been previously.

Someone will be able to explain this better than I can right now but the short and dirty version is that actual banks in the US operate with authority given by the federal government. This relationship grants them perks like being able to operate across states lines, etc., but also FDIC protection which insures the deposits they hold for customers. Since marijuana is illegal at the federal level, banks cannot have customers who are in essence violating federal law. Allowing dispensaries to be customers opens the bank up to a level of risk they are not willing to bear. My comment referencing being "federally insured" is in reference to FDIC, which is the easiest way to tell whether or not a bank is regulated at the federal level. Many credit unions are in fact not "banks" in the traditional sense as they are not federally regulated and do not offer FDIC insured deposits (although IIRC there is another form of deposit insurance that is not federally backed). So again, the short version is your payment path in the marijuana industry cannot touch any corp that is federally regulated.

> Federal government says it's not illegal

Pot is still illegal at the federal level. Though the Obama-era DOJ deprioritized enforcement. Jeff Sessions just rescinded this policy. So I'd expect to see some new cases dealing with pot end up in federal court.