I do feel that we are declining, and fast. We are so profoundly divided now that words like compromise, coalition, and working across the aisle became foul words and the people who tried to employ them were immediately branded RINOs or DINOs by their own peers, and became pariahs. What a party tries to accomplish when that party gets to power, the other party tries to destroy as soon as the other party gets to power. This leads to political paralysis and we don't accomplish much, while other countries continue to advance. Our problems are piling up, and are worse than it is apparent, because by virtue of still being the owners of the world's international currency and having the world's most powerful military, we appear to be doing better than we actually are, with our growing debt and deficit. And both factors that still prop us up won't last forever.
Like all empires in human history, we will fall. I pity the next generations.
I believe that either a parliamentary system or a true multi-party system might fix our political paralysis (the former would be more flexible, and the latter would restore the need for compromise and coalitions), but I'm fully aware that neither will ever come to pass, or at least not before we finish our decline.
All the above is internal. In termos of geopolitics, the external factor, I believe that a confrontation with China will become inevitable in the next few decades. China clearly aspires to be the next dominant superpower, and while they still see us as useful commercial partners, in the near future they will see us as an obstacle that must be taken down.