The latest guessing game is whether Donald Trump will drop out of the presidential race before Election Day. Although his campaign has denied that this is a possibility, ABC News reports that senior Republican officials are taking the idea seriously enough that they are exploring how to replace him if he drops out.

So, what are the odds he quits?

One way to determine this is to look at the latest odds in political prediction markets. It’s not that any bettor knows what Mr. Trump will do. Rather, markets are useful because people putting their money where their mouth is are more likely to give an honest assessment than party insiders positioning for political advantage. Moreover, aggregating the intuitions of many traders usually beats relying on any group of pundits.

At the British prediction market Betfair, traders currently assess the Republican Party as holding a 25.8 percent chance to win the presidency. But they give Mr. Trump only a 24.1 percent chance of becoming president.

The difference of 1.7 percent probably reflects the possibility that Mr. Trump drops out and that an alternative Republican wins the White House.