I think he would actually have to be more aggressive about moving his money to get it taxed. As long as his wealth is mostly in the form of unrealized AMZN capital gains, it won't be taxed.

Regardless, even though the US government accepts donations[1], they typically have to be given without restrictions[2]. So he could donate $2b (or sell off enough shares to pay $2b in taxes) but the impact on the HLS budget would probably be negligible. Making a contractual change is probably the most effective way to get NASA a second lander option (except perhaps hiring a bunch of lobbyists)

[1]: For example, https://fiscal.treasury.gov/public/gifts-to-government.html

[2]: a few very specific parts of the government actually are allowed to accept restricted gifts, but NASA is not one of them. IIRC this caused issues when they were looking at selling naming rights for launches and payloads

I presume doing so wouldn’t fulfill his belief system (exceptionalism, self made person). SpaceX should, imho, hire away whomever is left at Blue Origin (look at their Glassdoor reviews) just to kill this drag on their efforts (having business people trying to compete with lawsuits and back room deals instead of engineering after they’ve lost the contract). Pay them to hang at the beach at Boca Chica if they need garden leave to avoid BO litigation.

Do you think this tax money will be spent on NASA? I would wager not.