Of the many theoretical shenanigans made possible by time travel, towards the top of my list would be this:
Late 1933. American Prohibition has just ended. I walk into the beautiful, brand-new, Neo-classical Las Vegas courthouse and post office building, approach the nearest official, and smile winningly.
I inform them that in fewer than 100 years, their basement—yes, this very one—will be home to a government-endorsed functioning speakeasy, complete with in-house moonshine operations.
I just want to see how they’d react.