Other democratic countries don't have the influence and power that the United States does (for better or worse).

Consider the Cold War (which really wasn't that long ago) where there was a real possibility of the destruction of the country, or 9/11 where the country banded together to fight a perceived threat. Keeping the United States as a top world power is obviously going to be of interest to Americans, and national defense is a part of that.

> Do US citizens honestly think National Defence os a top priority above all else? If so, why?

Ultimately, being able to guarantee that you can defend yourself ensures you can seek out your other values in life, whatever they might be. In fact, I'd argue that many countries have the privilege to not even think about their national defense too much because they rely on American military guarantees for protecting their borders and trade.

Americans certainly do quibble about the size and scale of the American military machine and its role in the world though. This is a very frequent topic of discussion in political discussions with a number of friends.

Because they don’t have to as long as they are under the US defense umbrella.

Go back a hundred years and "national defense" was just a part of European culture. What's changed is that in the post-World War period, Europe was necessarily domesticated (aside from the UK and France) and made to be solely dependent on the US for all geopolitical and defense needs. The UK absolutely still talks about national defense issues. Germany chooses to ignore the issue because for the past 70 years, the US was tasked with dealing with these pesky minor details and Germany could pretend that any global geopolitical issues could be solved with pacifism and trade deals.

Those democracies are protectorates

The greater the military budget, the more you have to justify it.

Above all else? No, but it's definitely a top priority.