The purpose of the Second Amendment was to prevent the standing army from being used against the citizenry. The idea is a little archaic today because royal families do not maintain their power via their own private armies, and we never accepted the idea of royalty here anyway, but the division between civil and military authority is still enshrined in our Constitution and laws.
The Second Amendment would probably not be the issue that it is today except for the Civil War and the intense lawlessness that followed. It was during this period that names like Colt, Winchester and Remington became household words and guns became fixed in the American psyche as symbols of freedom. (Which puzzles the rest of the English speaking word.)
Biden is a life-long politician and probably understand that elections here are decided by moderates and that you only have to anger a tiny fraction of them to lose the next one. But we'll see...