You baseline that stuff and then add additional boxes you can check. California does it as additional “gifts” but the federal return does it already for the presidential slush fund. You could increase that more - add a 1% tax but you get to check a box and determine where it goes.
Mathematically it wouldn’t do much but it would make people feel more invested I suspect.
Fun fact: the US Treasury accepts donations to pay down the debt: https://www.treasurydirect.gov/govt/reports/pd/gift/gift.htm
You can also donate to the general fund: https://www.fiscal.treasury.gov/public/gifts-to-government.h...
