I can think of at least one in recent memory. But really, have you not been paying attention? They all do that. I'm not saying you shouldn't hold a politician accountable for coming up short in the promises department, but promising shit they have no idea how to deliver is how they all get elected, because so many people are so goddamn stupid and refuse to be skeptical. It's like steroids in athletics. They basically have to do it at this point to have a chance to win.