I don't know where I heard this, but a Liberal Empire like America is a contradiction in terms and in order to function it needs an enemy. The USSR was perfect while it was around, and then there was some thought that the US could make global security or terrorism a couple of windmills to tilt at and to maintain the Empire - but nothing's worked. So, the hope is China or Venezuela or Iran or Russia or any nation-state can play the role and they're starting to get desperate in getting public buy-in.