Decline (99 times out of a hundred) is so slow and steady that the only way to discover that it's happening is to compare things NOW with things THEN.

So: Can a single-earner family today buy a house, a car, and send their kids through a good education system?

Is the US still capable of launching men into space, let alone sending several at a time to the Moon and back safely?

Can a normal wage-earner still afford several weeks of hospital care?

50 years ago, we would be answering 'Yes' to all three of these questions.