Well, since we have much more information about presidential elections (which happen regularly) than we have about brexit (which is mostly without precedent), you could argue that election 2016 forecasts are probably more accurate.

I don't think that's the case though. I predict a Trump victory on the basis of a very strong social desirability bias and an immense amount of silent resentment against current social justice orthodoxy, especially as it pertains to speech restrictions on campus and in the workplace.