If I were President
This is a very ad hoc collection of ideas by a European guy who does not know all details about the inner workings of the political system in the USA. I am also aware that one person could not just change everything. - Except it would be a situation like in ancient Athens, when everybody knew that things went downhill, and they asked Solon to design a new system.
1. Let as many competent people as possible decide about the most important issues
The wisdom of crowds can produce better decisions than a single genius. I would ask the people to decide the most important matters: constitution, health system, currency, declarations of war. However, those people would have to prove some understanding of the matter.
See James Surowiecki's book: https://www.amazon.com/-/de/dp/0385721706/
2. Stop all wars!
It seems like the USA is at war all the time. Those wars have led to a lot of disorder and millions of deaths. The USA should obey the rules by the UNO - like most other countries. The USA should also start a reform of the UNO, with the main goals of avoiding wars and spreading good practices like freedom of speech and freedom of religion. NATO should be a defensive alliance and do just that: Help members that are directly attacked.
3. Create a reasonable health insurance
It is just crazy that some doctors make millions while average people's lives can be ruined when they get ill. Take a closer look at the health system in Britain or most countries in the EU.
4. Freedom of speech is really important
Everybody should be allowed to say everything, except direct calls for violence or insults. This should also apply to the media that have become public places of debate (Twitter, Facebook). People with unpopular opinions should be debated, not harassed.
5. Reduce public regulations and authorities to a minimum
Get rid of all unnecessary rules and the bureaucrats who oversee their application.
6. Provide cheap housing for the masses
+ the very basic needs of food, water, electricity. Even people who just don't want to work should be able to live on a very basic level.
7. Give incentives for people to build wealth
Teach it in schools, don't tax private houses
Would it be possible to only collect excise taxes and get rid of income taxes altogether? However, the most rich companies should pay some taxes. The enormous amounts of money that are moved on the stock exchanges should also be taxed.
The system should be simple enough that everybody is able to fill in an income tax report. As long as an income tax is necessary. ;)
9. Environmental protection
Clean air and water and also natural resources like the soil, the oceans and the forests are vital. The state should keep a close eye on them so they don't go to waste.
10. Reduce the powers of political parties, NGOs and religions
Such organizations don't bring out the best in people. Personalities and experts should play a bigger role in the political process than parties that are driven by ideologies and mutual favors. Political actors and activists who incite different groups against each other should be stopped.
11. Freedom of religion is mostly freedom from religion
Some of those communities put a lot of pressure on their members. The state should keep a close eye on them and pat them on the back if need be.
12. Only allow people who bring something to the country to immigrate
Huge population growth due to immigration worsens the quality of life in a country. Instead, you should make sure that the people who already live in the country get along well with each other. Permission to immigrate should be an honor.
13. Give incentives to have some children
Family is more important than career. And help parents raise their children without violence.
14. Reduce the roles of cars in daily life
It should be possible to walk to work or take a bus or a train. Something like the TGV in France.
15. More people in the economy should MAKE things
Cars, computers, but also furniture, food, crafts. Reduce the share of bullshit jobs.
16. The central bank
A great strength of the USA is that it can print dollars. This supply of money should be managed by people who are democratically legitimate (and professionally competent). Whether an independent central bank is really possible seems doubtful to me. In the conflict of interests between a heavily indebted state and the citizens who want a stable currency, I would prefer the interests of the latter.