I feel like we need to get our act together a bit. We're not in the hole yet, but we're definitely headed there, and that can be seen from both international and national politics.
Allow me to explain a bit further. We, as a country, have the potential to do a whole lot of good in the world. We still have the most powerful economy and military in the world. China may be bigger and have more people on both fronts, but it doesn't have all the gears working quite like they should yet, and that likely won't be completely fixed for another twenty years. No other country can come close to having the sheer power that America has under its belt. The problem is that there isn't a set goal for the whole country. It's pretty easy to see where things started going downhill: Vietnam and shortly thereafter was the starting point, but the ball didn't truly get rolling until the collapse of the Soviet Union. That left the US without someone to face off against, and it stagnated. Countries, like individual people, often need a solid opponent to duke it out with in order to stay competitive. Being numero uno only lasts until someone else sneaks up and takes the title from you, and often when that happens you're too late to take it back. America built its way up to the top, and now that we're here we have nothing to do, so we bicker between ourselves and cause more trouble.
Notice how, for a couple years after 9/11, the country stopped stagnating and started getting itself in gear again. This lasted until the people lost interest, the leader began to make poor decisions, and we went back to what we were. For a few years there, we had a common enemy and we rallied. Now, I'm not saying we need a war to keep us going. That certainly would be the easiest way to get ourselves back in gear, but it would also be one of the worst. The same effect could be achieved through having a non-military rival. For this, it's likely we'll need to look towards China or Japan. China would present much more of a military threat, and is likely the next 'opponent' the US will pick out, but Japan is a production superpower in itself; it has about the same landmass as California, but has half the population of the US and half the production power. If they had more territory in which to expand, they would have surpassed us years ago. The European Union wouldn't be a bad rival either, but the fact of the matter there is that Europe has been in a similar decline since the late 1800's. It's not yet unified enough to present a solid front that could actually rival our power, and it probably won't be for another 40-50 years.
This rivalry doesn't have to take on the form of another country though. If the United States had a set goal, and a reason to push towards it, we could get something going. That, however, has to be something big, something that requires the majority of the US to work on it at once. Getting to Mars would be a good start, but better than that would be setting up a permanent base on the Moon. The ISS is a good step and all, but it's doomed to fall in to obscurity from its very design; it's not built for expansion. I could go on this for hours, but the short (or not-so-long) of it is that we need a big step towards space exploration to get us moving again, because the issues on Earth are isolated and don't affect a large portion of the population.
Since I'm on a roll, I might as well go a bit in to US politics. In short, however, they're stupid. Too much infighting, both between the two parties and within the two parties, has caused things to end up stalemating back and forth repeatedly. In all likelihood, Obama will last through his second term and then a Republican will take back control and the pendulum will swing back to the Right almost completely before swinging back. The almost complete re-coloring of the Senate and Congress every 8(ish) years makes whatever the last President did almost completely useless; if things would stabilize a bit and people would stop thinking in straight Red/Blue we would be able to continue moving forward, or at least make it easier to do so. If it keeps going the way it does it'll be a tossup to see whether a civil war breaks out before the economy collapses on itself or we get invaded. None of those options sound pretty, and they all affect the rest of the world greatly, which is a large part of why the entirety of the rest of the world is so focused on us; what we do affects everyone else almost as much as it affects us. Good or bad, it's one of the effects of continuing globalization, and it'll only get more pronounced as the world becomes more and more interconnected.
And I should probably stop there...
TL;DR: The US has the potential to do good things, but we need to get our shit together before we can do so. That could mean uniting against a common enemy (or rival), or it could mean setting a national goal for ourselves and going for it (space exploration). None of that will happen until our politicians get their heads out of their asses and start working for the country instead of against each other.