That figure, via to the Iowa Electronic Markets, represents a bigger chance than any other presumptive nominee in recent history. Below are the IEM selling prices for all of them since 2000 (excluding incumbent presidents) from the same period before their national party conventions.
Traders also currently see about a 4-5 percent chance Hillary Clinton isn't nominated by Democrats the following week -- perhaps because of her email situation or a Bernie Sanders refusal to drop out and formally endorse her, or maybe both.
The only candidate in recent years whose nomination was preceded by that level of doubt was John McCain, who was trading about where Clinton is now at this juncture in 2008. Everyone else has been at 97 percent (rounded up for George W. Bush) or above.
We could get into a whole discussion here about how predictive political futures markets are, but that wouldn't be any fun. For now, just know that Bill Kristol isn't the only one who thinks #NeverTrump still has a shot at success.