Hello:

Does federal law supersede state law inside a "federal" office building located in downtown Seattle??

excon

For most purposes, no.

Why? Because it depends.

Hello again, lawyer:

Let's say marijuana was LEGAL in Washington, but ILLEGAL as far as the feds are concerned... So, somebody visited the aforementioned federal building, and upon going through security, it was discovered that he had some marijuana. Can the federal police arrest him??

Well, of course they can, and it doesn't matter whether he's in a federal building or not.

Never mind.

excon

You got it.

Possession of grass is a Federal Crime anywhere, in Washington state or any other state. Just because those hippies in Olympia think they can change the state laws which made it a crime doesn't mean that the Federal laws on the subject are in any way affected.