As I and others have opined in the past, the post-WWII boom years created a perfect storm for the USA. Pent-up demand for goods, coupled with the USA being pretty much the only economy standing, allowed a large middle-class to form, and fueled the "baby boom". The GI Bill sent large numbers to college for the first time, giving us an edge in technological development. The Cold War and the Space Race, then later the Electronic/Internet Age did the same.
In the meantime, Europe and Japan re-emerged, followed now by Brazil, India, China, etc. And the baby boomers here got old, and are now on the the waning side of productivity, and the generations behind them are smaller in numbers, and are burdened with looming SS and Medicare "bubbles".
I think we've collectively borrowed from the future by not matching government revenues to spending, by mortgaging to the hilt for "stuff", and by punting all this further and further down the road, rather than "fixing" it. There's a drag on the economy caused by all that debt, and and many of the gains of the past twenty years were "juiced" by all this can kicking. So, expecting the same growth going further is a tenuous proposition...
Having said all that, we still have a large and growing economy, US companies are participating in the growth of the BRICs and other, we still have some of the best universities in the world, our population is growing, especially compared with Europe and Japan, we have previously untapped energy resources coming on line, etc.
It's not all gloom-and-doom, nor is it all sunshine and lollipops. Let's call it recency bias for a period where many of the stars were aligned, and expecting that exact same scenario (anomaly?) is probably wishful thinking. But, we are in a good position to hold our own, maybe even excel, in the current and likely future environment...
Sorry you asked?