You asked a question, "What made America great?" and you also made reference to Ronald Reagan. I am going to address your question but I am not going to address Ronald Reagan because I don't think he's relevant to your question, though he was a great Statesman for his time. The reason that President Reagan is not relevant to your question is because none of America's 47 Presidents to date are responsible for America becoming "great' in the first place.
When America was made 'great' was at a time when it's new-found freedom was established after the Declaration of Independence was signed by all parties concerned, including the King of England who formalized America's divorce from Great Britain on September 3rd, 1783, not the 4th of July 1776.
Yes it is true, Americans declared themselves an Independent Nation on the 4th of July, 1776 but that was only America's opinion of who they were and what they were all about and where their minds were at collectively!
In the minds of the early settlers of America, they thought they were the one's who called the shots, not the King of England. But the King held the deed to the ranch, so it was actually the King who called the shots and not all those rebellious 'commoners' who thought they out-ranked the King of England.
Great Britain still had to agree to America becoming an independent Nation and it took another 7 years before Great Britain formally 'ALLOWED' the 13 colonies of what is now the United States of America, to in fact become independent of Great Britain.
It was at that point that Great Britain handed the 13 colonies of America the deed to it's inherited ranch. It was therefore the 3rd of September, 1783 that America WAS GRANTED it's Independence from Great Britain, BY the King of England.
That being said, when Americans now speak of "freedom" and living in the land of "The Free", those quoted words generally apply directly to the United States of America because of it's historical past involving it's past relationship with Great Britain, though every other country in the world that is not living under a Dictatorship regime, enjoy the same level of "freedom" that is otherwise usually only ever made in reference to the USA, simply because of America's tumultuous past and it's relationship with Great Britain.
"Freedom" from the King therefore, was a huge deal at the time, whereas freedom in most other free Nations was not as sticky an arrangement as was America's relationship with the King of England.
What "freedom" actually means in the USA (and everywhere else I mentioned for that matter), is the unrestricted ability for that country's citizens to grow and prosper at their OWN will, not at the will of a King; to become whatever they want to become when they 'grow up', not what the King wanted them to become; to fly as high as their ability and ambition would take them and not have altitude restrictions imposed onto them by some narcissistic King who's never been part of the action on a different continent, thousands of miles away.
When America was under the thumb of the King of England back in the 1700's and a large portion of everything that America ever earned on it's own..$$.. was sent home to the Mother Ship called Great Britain who pretty much dictated how much they'd take for the Crown in the form of 'taxation' ...and how much those annoying peasant Americans would be allowed to keep in their pockets which was called 'after King's income', which of course became America's net income.
What made America great was the freedom of Will for all concerned that followed, after the King of England cut America loose and wished it a safe voyage, though he didn't really mean it because he was a prick at the core of his being. The freedom to choose, the freedom to grow, the freedom to prosper at one's own Will is the definition of "Freedom" and is what makes a country great for it's citizens to thrive in.
What made America great therefore, was nobody standing it America's way as it grew and prospered on it's own, in ways America saw fit for all concerned who lived in the country for the next 240+ years and of course beyond.
That is why it was nothing specific that we can put our finger on, nor was it a specific date of recent times that modern day Americans can reflect back upon when looking for that 'state of greatness' that somehow got left behind, because what made America great was it's new-found freedom after those first few brave souls broke away from an authoritarian King who saw himself as Supreme Commander of the world and beyond, according to the legend he created of himself in his own mind.
That is why the United States can't go back to a time when America was 'great' because that time in question is actually the 'present moment', not the past!
When the day comes around again that Americans will no longer be restricted in their movement nor prevented from growing while being subject to the changing whims of an authoritarian government, only then will America be great again, just like it was in the beginning. But that does not necessarily mean that America isn't there already... or is soon to be! 🇨🇦 🇺🇸