Capital flight is not a thing. US dollars only exist within the US banking system and the Fed, so they are never out of reach. However, I think you missed the point of taxation, which has never been to "fund" spending at the federal level. The US dollar is self-funding when it is created and no one's taxes are used for that. Taxation destroys money in the private sector by reducing the debt. End of the story of the dollar which is never recycled for any purpose.