Former U.S. Defense Secretary William Cohen says President Donald Trump is a "disruptive force" in politics, and his unpredictable behavior could undermine his own administration. "I think it's an inconsistency which causes our friends — and our Chinese friends are included in that — to worry about whether we have any kind of continuity in policy," Cohen told CNBC's Eunice Yoon at the China Development Forum in Beijing on Sunday. "That kind of inconsistency undermines confidence in the administration," said Cohen, who served as defense chief under President Bill Clinton from 1997 to 2001.

I think most countries would like to have some level of predictability and continuity — and the president seems to thrive on not being predictable. William Cohen Former U.S. Defense Secretary

The U.S. Treasury Department blacklisted two Chinese companies on Thursday, saying they helped North Korea dodge U.S. and international sanctions. Those measures are aimed at pressuring North Korea to dismantle its nuclear and missile programs. But in a move that surprised and confused many, Trump tweeted on Friday: "It was announced today by the U.S. Treasury that additional large scale Sanctions would be added to those already existing Sanctions on North Korea. I have today ordered the withdrawal of those additional Sanctions!" Trump tweet: It was announced today by the U.S. Treasury that additional large scale Sanctions would be added to those already existing Sanctions on North Korea. I have today ordered the withdrawal of those additional Sanctions!" The president's tweet led many to conclude he was overturning Thursday's sanctions on the Chinese companies. However, some media reports indicated that Trump might have been referring to future sanctions. The White House has not responded to CNBC's request for clarification, which was sent outside office hours on Sunday. "If you can have the Secretary of Treasury impose sanctions to be reversed by the president the next day, that causes, I think, some question about our reliability coming out of the administration," said Cohen, who's now chairman and CEO of consulting firm The Cohen Group.

What's next for North Korea?