Right, let's start at the top.
China invading the US?
No. Not going to happen. The PLAN isn't powerful enough to support the supply routes needed to sustain an invasion of America. Furthermore, the attrition rate would not be worth the effort of invading.
In WWII, the Japanese contemplated the United States, but only briefly, they realised it would be a doomed effort, because the IJN couldn't support such an invasion and the IJA would struggle to control the areas under its control. The same problems are put forward by China invading, or indeed ANY nation invading the US.
So, a combination of nations? The Russians and Chinese perhaps?
Nope, still not enough and again supply problems would make any invasion grind to a halt not far from the seaboard.
The enemy carriers would be a key target for US attack, as would any coastal airfields that are captured. Robbed of key air cover, the enemy ground forces would be subjected to daily air attacks from every corner, up to and potentially including tactical nuclear weapons, chemical and biological devices. Their landing zones would be bombarded mercilessly from air and sea and their supply ships sunk in droves. Mass desertions would begin as the invading army ran out of ammunition and food (although some could continue functioning for a short period using captured food and weapons from the local populace, but eventually they too would be faced with an opposition they couldn't counter).
The only advantage the enemy would have in the initial attack would be the element of surprise...however, this is not Pearl Harbour any more, the US has a better intelligence network and it's not easy to hide a carrier fleet from things like RORSATs.
They could use merchant ships as a cover, firing ballistic missiles into an altitude high enough to create mass EMPs across America, this would create pure chaos, but primarily amongst the civilian populace, the military would fare better and eventually be able to counter the invasion for reasons mentioned above. However, the effect on the civilian populace would be pretty devastating and there would be a LOT of deaths from lack of medication and health care, and a lot more from people failing to adjust to a situation where there is no electricity. However, the retaliation against the enemy nation would be just as devastating and perhaps lead to a full scale exchange, in which case a lifetime without electricity would be the civilian populaces smallest problem.
Once the element of surprise is lost then so is any invasion of America. It's too big, too well armed and the populace too prone to uprisings. The Soviets couldn't have done it, the Japanese couldn't have done it, we tried and failed at it, so the Chinese certainly wouldn't consider it. Besides, the Chinese don't generally act against nations outside of their sphere of interest. If they wanted to attack America they might missile the shoreline cities from SSGNs or perhaps detonate bombs in cities through espionage and gangs...I imagine the triads might be willing to assist the PRC, but an actual invasion...no, it's not their doctrine. If you lived in Vietnam or Taiwan, then I'd say that you might have something to worry about, but in America? Nah, ain't happening.
Still, it makes for a good film for the masses that don't know any better, stirs up the patriotic spirit and all that.
By the way, Red Storm Rising, as excellent a novel as it is, is inaccurate in one major factor. The absence of nuclear weapons. The Soviet and NATO war plans of the period involved the liberal use of nuclear weapons from almost day one, particularly the Soviets. They would be used to clear a way through NATO defences and paralyse their airforce and command structure. Of course, as soon as the first mushroom went up, NATO would retaliate, the escalation ladder would be climbed and eventually World War III would consist of a handful of Soviet and NATO troops wandering around a nuclear wasteland.
All this within about three or four days.
Obviously this makes for pretty poor reading material, so most games, books and films take the nuclear weapons out of the picture until such a time that the armed forces have had their fill of action.
There is a chance that neither side would want to use nuclear weapons first, however generally speaking within a week or two of fighting, someone would have resorted to it. Either NATO to stop the Soviets, or the Soviets to make a breakthrough as their invasion begins to overstretch and run out of steam. Failing that, West Germany would have surrendered before the nukes came out, fearing the total destruction of Germany as a whole. Better Red than Dead and all that.
It's still a good book, and certainly one of Clancys finest, alongside HFRO, and certainly if a number of factors fell the right way then it could be a realistic look at a Soviet invasion of West Germany, however it would take a great number of things to fall the right way for the original plans to be altered so much.
Take a read of 'Chieftains' by Bob Forrest-Webb, you're probably best doing it through something like Kindle because the going rate for the original book is a stupid amount of money, but it has a fairly realistic look at WWIII, that is to say, it doesn't end well.
Here's some more recommended reading:
http://www.worldaffairsboard.com/fie...a-austria.html
http://www.jrnyquist.com/may14/ussr_war_plan.htm
http://www.pprune.org/archive/index.php/t-447673.html