The United States is a mature economy, but just because it is so well seasoned, does not mean that it cannot produce envious economic growth in comparison to other nations, but it does not. The systemic problem that has only gotten worse in modern times, is not that America lacks innovation, and not because America lacks capital, and not because America lacks an entrepreneurial spirit, but rather, that despite all of these good attributes, America cannot create impressive economic growth, because it lacks fundamentally a fair distribution of the profits, income, tax burden, and wealth that this nation and its people so generates.
That is to say, in recent years, the richest of the rich, have gotten so much wealthier, that they have effectively sucked capital and income out of the hands of their own citizens, to thereby have it exclusively in their own hands, of which the national government as well as state and local governments, have been to a very large extent, aiders and abettors to those that need no hand-outs in order to conduct their affairs, yet, are provided with all sorts of favoritism by those governments, again and again. This so done, has permitted more and more capital to be concentrated into fewer and fewer hands, of which, those that have that capital, which is typically taxed at extraordinarily low rates, have nowhere to put their money to use, other than passive investments into equities and the like, because there isn't any good point in their increasing capital investment in their factories or even of research and development, when the target audience for the products or services so being manufactured or created, don't have the ready funds to purchase such.
After all, when the superrich, have all of the money, there are only so many homes, so many cars, so much food, so much healthcare, so much education, and so many material things that they as individuals or as extended families can sanely purchase; of which, the balance of such money is thereby passively invested, so as to make even more of it. On the other hand, millions upon millions of Americans, if they were to receive a living wage, or were provided with better opportunities so as to make a decent and sustainable income, have a real need for the essentials of life, such as a good home, a reliable vehicle, good food, sensible healthcare, and a proper education, so that they can live a good life.
The bottom line is that despite all of the printing of money by the Federal Reserve, that the mere printing of such money and then thereby the distribution of that money first and foremost into the hands of those that are at the top of food chain, will not and does not ever trickle down to those that really need it. Instead, what happens, is that as the wealth disparity between those that have and those that have not creates an ever bigger chasm, this effectively slows down the economy to a crawl, because sellers can't sell more goods and thereby won't invest even more money into their businesses, when the targeted buyers for such, are essentially broke.