There have to be a lot of things going bad for a major war to happen. War is probably to start out in Turkey, trying to get back a chunk of the middle east back. Russia is always ready to oppose the status quo and get back influence in Eastern Europe. They do not stand a chance against the US.
Even if China sees this as an opportunity to jump to (that's a VERY big if), the US can easily handle all three of them. The problem is going to be whether or not the US can count on its allies in Asia. Not because it needs the military support, they don't, but because you cannot be alone vs. the world. The population will simply not support you.
As it is stands now, the US can count on its allies in Asia. No matter how much they dislike the US, they fear and hate China much, much more thanks to thousands of years of history.
The status quo might change but not violently, perhaps giving influence ground in Eastern Europe and the Middle East. Also losing ground in future trade/economy deals which will have a real impact on US population if it were to happen.