For five years I lobbied Congress to get more money for a project I was affiliated with. I never succeeded.
Aaron Wildavsky wrote a book on how Congress does its budgeting. The book originally sold for over $100 a copy and Aaron made a great deal of money because 4,000 lobbyists and 2,000 members of Congress and their staff bought the book. No one understands the budgetary process.
What I learned, while lobbying, is that there are 13 different budgets presented annually by the Executive to Congress. Most never get passed, they get a continuing resolution which means the departments in that part of the budget continue spending what they got the previous year, sometimes with a modest inflationary increase.
That is why all the war budgets, Iraq (both wars) and Afganistan get separate budgets, and approvals, every year. They would never be funded if they were part of the standard 13 budgets.
I have no idea how many actual total budgets with all 13 components have been passed with genuine modifications in the past 20 years, but I'll bet the number is close to zero.
This also helps you understand pork-barrel set-asides. They are necessary exceptions, bribery, to get any parts of the budget passed.