2 former US Treasury Secretaries just shared the biggest risks that keep them up at night

Business Insider is at the SALT hedge fund conference in Las Vegas for the next two days, and the first session just kicked off.

On deck were former US Treasury Secretaries Robert Rubin and Larry Summers. David Rubenstein, the co-CEO of Carlyle Group moderated.

And of course, Rubenstein asked the two gentlemen a derivitive of the most important question of the conference: "What is the biggest risk to markets you see outside the US?"

Remember, as with all Wall Street conferences, we're here for a long hard risk assesment.

So here goes.

• Rubin said that his big worry is China. He said that when you get Chinese economists alone, they can speak candidly, and admit that they're more uncertain about the future.
• China has reverted back to relying on investment to stimulate growth. "I'm not saying where it will come out, but I'll say there's a lot more complexity to come out in the shorter term," Rubin said.
• Summers also put China on his worry list, saying he sees a lot of risk there over the next three years. He also deviated a little bit from the topic and turned back to the US.
• "Political risk driving huge economic risk is something that I always thought we talked about in connection with emerging markets, and now I think it's something that could happen in the US," Summers explained.
• "Populism taking over and leading to huge instability... I don't think it's a great risk but I think it's a risk that's not priced in to markets."

And truly, it's the risk that isn't priced in, big or small, that will hit us the hardest.