Well in recent decades the US has been increasingly sliding towards and embracing far right extremism, corruption, anti-democracy, anti-rights, anti-education, and attacking the rule of law and the constitution.
If something doesn't stop that corrupt far right extremist insanity, this is gonna be the century in which America goes from super power to an increasingly unstable and failing nation. By a few hundreds years America certainly wouldn't exist in any form we know it as today.
But that's only if we keep going down the republican path (which of course Trump has jumped us forward by probably a generation).
If good people and the rule of law and the ideal of America prevails, we'll claw back the dream and crush all this extremism, insanity, and corruption, and the US may remain a leader in the world.
Then again, a few hundred years is a long time. Even if we destroy 21st century republicanism and keep America going, there's still the fact that the US, and the entire world, is in a huge financial hole that will eventually lead to an enormous monetary crisis, which will in turn cause huge financial hardship and economic depression for the population, which may result in revolt, and could lead to America falling at some point in the next century and who knows what will rise up from the ashes.
Then there is also climate change which will decimate many areas of America. Maybe the country would keep going but life will get much worse overall for much of the population.
So there's three major threats. 1) The immediate and continued right wing political extremism/corruption that has just been getting worse and worse the past 3 decades and is the most serious problem in the US at present day. 2) The impending fiscal earthquake that has been building since the beginning of this century and which there is seemingly no way out of and will eventually cause massive problems, of which we already are seeing effects but major serious effects are likely still decades away. 3) Climate change if the world doesn't get super serious about it in the near term, of which we are of course already seeing effects and those effects will build to catastrophic proportions over the course of this century.
What's the likelihood we stop all three of those things? Right now it looks like the rest of this century the US is just gonna keep getting pounded worse and worse by all three of these things. So the fall of the US I think honestly is fairly likely in the next century. Even if it doesn't actually collapse, the US is likely to be far weaker, far less free, far more corrupt, are far less economically prosperous in the future. It's bleak, but realisitic. Those in power are too busy squabbling over increasing their own power or short term quarter by quarter or election by election issues to deal with such issues.