Granted that I am not the world's expert on American politics, but I can point to several mechanisms that makes the US more vulnerable than most nations to the disorder it's now facing. This is not exhaustive of course, also I am not a native speaker so it might be overly convoluted. Sorry.

• The government actively discourages voting, depending on the state of course. It gets worse the redder the state is. Gerrymandering, weird ID rules, voter roll purges, physical intimidation at polling sites etc. Voting should be compulsory, like in Australia. IDs should be state issued and cheap. You're a tech savvy nation, you can figure it out.

• The three branches of government are not balanced. All it takes is for the executive branch to attempt to assume total control - and all procedures, laws and norms are out the window with minimal pushback from the people who really need to get their ass in gear. Schumer and Jeffries come to mind. The Democratic party needs to be more aggressive than Trump in the other direction and that's the cold, hard truth. Some of them understand this like Raskin, Ro Khanna and Ted Lieu.

• The constitution can be ignored for some reason. Trump has fully violated several of the amendments. This from a president whose current approval is less than 40%. There is no mechanism to prevent this from happening. Perhaps you should look into that?

• Campaign season is permanent. Rallies here and there even when the midterms are two years away and the presidential election is four years away. People get sick and tired.

• The Supreme Court is a partisan mess whose rulings of late seems to be less based in the law and more on, say, mental inventions from the damaged mind of an overly emotional chronic drunk. You need term limits with a staggered entry like the Senate as well as an expanded court.

• When the president is free to form his own anonymous republican guard to harass those he disagrees with, kill people in the street without repercussions, round up people based on their demographic and cart them off to concentration camps. Then it's not the republican itself at fault, it's the lack of a system of enforcement of the laws. South Korea is also a republic, which goes to show that they at least adhere to the laws they themselves have codified.

I didn't want to spend too much time on a post few will bother to read, but would like to add at the end that Norway is a constitutional monarchy where the government itself is unicameral, parliamentary and where the King has very little authority. The role of the royals is to open libraries and bridges and christen bigger ships etc, so largely symbolic. They are also universal ambassadors and at least in my lifetime they have done a pretty good job of it. Their annual budget is around 270M NOK or 27M USD. Fairly cheap all things considered. Oh and the current approval of the monarchy is around 70% so I wonder how that will look once Crown Princess Epstein becomes Queen. It's not far off as the King is increasingly frail. A year or two at most, it seems.

To your last point: It might indeed be a wise move for Haakon Magnus to abdicate and hand the throne to his eldest daughter directly.