The budget process described below addresses the piece of the pie labelled "discretionary" (31% in 2018). These programs are called "discretionary" because Congress must set funding levels for them each year through the appropriations process. In contrast, we have the "entitlement" or "mandatory" programs such as Social Security, Medicare and Medicaid (the 61% wedge). Net interest (8%) has crept-up in recent years and we expect that trend to continue, thereby taking away funds from the other categories.
Discretionary funds are categorized as "defense" or "non-defense." In 2018, non-defense discretionary (NDD) spending accounted for 16% ($642 billion) of federal spending (the other 15% of discretionary is defense related).
Science, environment, and energy programs constituted 16% ($100 billion) of NDD spending in 2018. Over half of the spending in this category (59%) functions as natural resource funding, supporting our national parks, and other environmental programs, including those in the Environmental Protection Agency. Just over one-third (34%) of the budget in this category covers science, space and technology related spending. Energy spending accounted for the remaining 7% of spending in this category.
Education, employment training, and social services programs constituted 16% (\$102 billion) of NDD spending in 2018. Out of the \$70 billion spent on major programs in the Department of Education (which includes discretionary and non-discretionary), roughly 33% ($23 billion) goes to post-secondary education programs, including Federal Pell Grants, which help students afford college. The Education Department's expenditure on higher education amounts to 39% of the agency's total discretionary spending.
The Budget and Accounting Act of 1921 requires the President to submit a budget proposal on the first Monday in February, although that process is often delayed.
The President recommends overall fiscal policy, with two main components: (1) how much the federal government should spend on public purposes, and (2) how much it should take in as tax revenues. The difference between (1) and (2) is the proposed deficit (or surplus). The president's budget is very detailed, and lays out his or her relative priorities for federal programs -- how much he or she believes should be spent on defense, agriculture, education, health, and so on.
The president's budget is only a request to Congress; Congress is not required to adopt his or her recommendations.
Only Congress can grant funding. After the President introduces a budget, it moves through House and Senate Budget Committees, working separately, to establish top-line numbers for spending, with input from other legislators, committee chairs, and party leadership.
To fund the government each year, Congress passes twelve appropriations bills. House and Senate Appropriations Committees take the spending target determined by the Budget Committees and divide it between twelve appropriations subcommittees (one for each of the twelve bills).
Of the 12 subcommittees, Commerce, Justice, Science, and Related Agencies funds the NSF (take a look at the House and Senate members, see if a member of your congressional delegation is one). This subcommittee's authority includes other science-related agencies such as NASA, NIST, NOAA, and OSTP, and also the Federal Prison Industries Incorporated and the Commission on Civil Rights, among other programs.
Once the differences in the respective House and Senate versions of the 12 appropriations bills have been reconciled, they are sent -- individually or in packages (referred to as an "omnibus" if all together, or "minibuses" if in smaller packages) -- to the President for signature into law.