The US being a shit-show is exactly why this job is so hard. You're constantly having to deal with political crap from Congress or the Supreme Court, state governors suing your administration whenever it does something they don't like, opposition pundits calling for your impeachment, and that's not even mentioning America's foreign affairs. There's a reason people call the president of the United States the "leader of the free world".

The US has a geopolitical position to defend and it's a never ending queue of foreign leaders clogging up your phone line and calendar book either threatening you or grovelling to you. And then there is the unique military position of being the commander-in-chief of the most powerful army in the history of mankind. So the president also has to attend military briefings, decide how to maintain and achieve the USA's foreign policy objectives using that army, whether to intervene in foreign wars, and so on. The US just has their fingers in so many goddamn pies that the job of president is unbelievably stressful. Yes, you're the most powerful man (or hopefully next year, woman) in the world, but with that immense power comes a humongous amount of responsibility. You could change the course of human history by merely scrawling some words on a piece of paper. You have the power to fuck up millions of people's days across the world with a stroke of a pen or by shouting some words down a phone.

You have to contrast this role with the leader of a country that is comparatively geopolitically irrelevant—their foreign policy is probably limited to dealing with the regional counterparts and/or the leaders of the USA, China, or Russia. The President of the United States has to deal with every country in the world because if there's one lesson we Americans will never learn, it's to mind our own goddamn business.

Just look at Obama—the man turned from a young energetic candidate to a ready-to-retire late middle-aged man after just eight years in office. Meanwhile, the prime minister of a country like Singapore governed two decades and is still in good condition to continue a career in politics.