Can anyone or any group defeat the US?
Right now, no way.
Are you talking about an invasion into US soil, or just a shift in the balance through non-military means? Either way, rigth now no chance.
There are powers that will be able to challenge the US, but to actually take it down thats another story. In the short term they may be able to pose a threat, but most things aren't solved in the short term, the US will win eventualy.
For a country or group of countries to be greater than the US they will need the following:
Natural Resources
Population
Industry
Economy
Hard working and Honest General Population.
Initiative
Inventivness
Good Sense (this is a hard one to descride, it basicly some sort of self perservation instict to not let its true ideals and culture be taken over, sort of like patriotism or belief in the establishment and furtherance of the country and its ways, or basicly not to let itself get so weak that it crumbles from within)
The US basicly has all the these qualities, which you can say helped to make it great. No country or group of countries posses all these qualities, thats what it will basicly take to top the US, but it must be done to a greater degree.
Other countries or groups may have the natural resources, population and maybe even industry. But they don't have the economy. The only proven way in history to have this massive powerful economy is through capitalism. So they must be willing to be capitalist.
But in order for capitalism to truly suceed they must have a hard working, honest population. This was fostered in the US from its founding by its religiuos Christian heritage, although it not as prevalent today, most aspect of its culture is influence by these traditions, for the most part at least. You will need a country with a traditional influrence of honesty and hard work similar to this to realize full economic potential based on a capitalistic system. Any other economic system simply cannot compete in the long term, for the short term maybe, but never in the long term. And those countries that try to achieve full capitalistic potential which don't have honest and hardworking populations will be severley held back due to lazziness, bad work ethics, and corruption (it will still work well enough to give its benefits, but not to a full and massive potential).
A correctly working capitalistic system will naturally foster intiative. This in turn will foster inventiveness, due to the fact that in order to compete in this system, products that better serve the interest of those same people supporting the economy will have to be made in order for those same people to want to get them. Thus you have what is called a virtuos cycle which propagates itself more and more, enlarging the economy.
Lastly is most of the population must posses somekind of good sense. Like I said this is hard to describe. Something similar to patriotism, but its more than that. More akin to sense of self preservation, to not let internal influences that would take your down or decay it into weakness, basicly to preseve the balance which made it great in the first place. Afterall alot of empires in history weakened themselves from within before falling.
The closest example that can successfully overtake the US as a world power would be the EU, but they lack two things, thats why they will never achieve it. Again they may do it in the short term but it wont last. The first thing they lack is intiative, their mostly socialistic system stiffles alot of this. Secondly is this "good sense" I was talking about, their shrinking population combined with massive Muslim immigration and births will results in total assimilation and takeover with 50 to 100 years. They no longer have this sense of self preservtion that will make them take the nesacery action. If the US follows suit as Europe then will fall too this is the only other way that someone can take over the US, if it decayed internally, but then it would be the US own fault, not because someone was greater.
So other than internal collapse, a country or group would have to have all those qualities I listed going for it to make that happen and beat the US. Frankly there is non that has, seriously if you look for yourself you will find none.
Maybe they can beat the US militarily and try to conquer it, but they will have to conquer the rest of the world first then take over Mexico or Canada or both, before they can invade. But the US will not stand by and let that happen in the first place. The enemy may get the upper hand in the begining but eventually they will have to face the full might of what the US economy and industry can produce, not to mention all kinds of secret and advanced weapons made possible by its initiative and inventiveness.
There will probably be other powers in the future to challenge the US, for the short term yes they may succeed even appear to win. But once everything the US has to throw into the fray gets in gear, watch out.