>but.. Um... what would you actually spend 2 trillion a year on for four years on to implement a change in society?

First I'd set some milestones for private rocket companies to hit that had funding payouts, think x-prize but considerably more money and tiered. I want to see something like BFR operational ASAP. In this scenario I'd actually try and 40% or so of SpaceX which would chew up 10 billion or more at their most recent valuation, this would allow for hiring more employees and getting more production capacity online. I absolutely one all of our eggs out of one basket, to do this we need to start having humans on other bodies to start seeing if living at reduced gravity is viable long term without genetic modification.

I'd do similar for the current companies that have expressed interesting in asteroid mining, on a smaller scale to encourage them to develop spacecraft initially testing ideas for tackling the problem. While mining asteroids isn't going to be economically viable for export to earth (although I think if we could drastically reduce the cost of rare earths and precious metals, we may spawn new technologies. Rare earths and precious metals may also be important for grid storage and renewable energy at greater quantities than are easily accessible on earth) but would allow for cheap construction in space as well as cheap fuel in space. Once we could figure out how to pull stuff off of asteroids, we could work on manufacturing technologies for microgravity.

I'd assemble several missions to Venus, the Moon and Mars. I'd send several identical communication relays to Mars and place some around the Moon for relaying data for both current and future missions to both bodies, I'd send several identical orbital reconnaissance satellites to all three bodies.

I would work with local governemnts to re-establish kelp and seaweed in coastal regions. This helsp reduce ocean acidification, provides safety for various marine species, helps to sequester some carbon dioxide and is a farmable crop.

I would work on deploying PV panels on roofs of public buildings. Think schools, government buildings, libraries distributed across the US to show people that PV doesn't need to be ugly and to considerably help distribute some power generation across the grid.

There's also a few people working on carbon sequestration I'd like to throw money at, but the amounts would be insignificant compared to a trillion plus.

This would easily chew up 1 trillion plus in 1-3 years just buying materials and paying wages.

I've ideas for many other sectors and avenues too but this gives you some idea that I could legitimately spend that amount of money. Some of it would be funding crazy research, some would be helping companies to expand current production capacity, a lot of it would be x-prize style stuff "hit a notable milestone, get more money".

I'd like to throw money at:

- understanding memory/the brain with the ultimate goal of backing up a brain

- exploring some fringe science for anything remotely valid

- find a use for our nuclear waste, so throw some money at companies like Oklo

- energy efficiency

- permaculture

- greenhouse growing to reduce all this importing and exporting of food all over the world. The US imports 40% of it's fruit, exports 40% of it's corn and similar percentages of other grain etc. Purely from a fuel standpoint this is baaaaad for the environment.

- encourage local manufacturing, I currently work in international freight and from publicly published numbers about our aviation jet fuel use it's mind-blowing how much carbon just my company produces each year.

- encourage more sustainable technology, socketed/modular upgrades for phones and computers

Etc