It requires a higher than average self-confidence and ego to want to be President of the world’s most powerful country. Carter was an example of a big brain and small ego. His chance of a second term was ended by the Iran Hostage event. Eisenhower was happy to retire but both parties pursued him to take the job. He had plenty of confidence but didn’t really want the job so his ego was almost non-existent.
Reagan had both with some administrative experience as Governor of California. It is the same with Clinton, with above average smarts. Obama was very smart but lacked the administrative and legislative experience of recent Presidents.
Bush I may have had the deepest amount of experience of any previous President. He knew how government worked and was friends with most world leaders. A few phone calls put Desert Storm Alliance together. He was a true moderate in the Republican Party.
Today we have a President that may be almost as knowledgeable as Bush I. President Biden was retired from the Senate and still grieving the death of his son who he wanted to be President. The party stalwarts talked him into running again to stop the left wing. He had the experience to bring back bi-partisanship and put the country back on track. The pandemic war shows he believes in following expert advice, reactivating relations with the rest of the world’s leaders, and fixing our economic problems.
With Biden we have the Carter ego and the Bush I moderation and experience. Most of Americans, and the rest of the world, are happy with the return of stability and reliability.