The data is not great here. It is from prices by bookies around the world. I have tried to find the lowest asking price for an outcome and highest bid price. But, bookies generally only list the ask price (i.e., how much they will pay for something). The true probability is lower than their ask price and higher than their bid price; if there is no bid price, than the true probability is between $0 and the ask price.
When will Trump stop being President of USA?