What Is the President's Budget?

The following excerpt from David Wessel's book, Red Ink: Inside the High-Stakes Politics of the Federal Budget (2012) (affiliate link), gives an explanation:

Every president since Warren Harding has been required by law to send an annual budget to Congress. It’s the only time that the chief executive of the United States has to make his promises add up. . . . The budget is one part rhetoric by the party in power that highlights—depending on the times—the government’s largesse or its tightfistedness. A second part details how the president would, if Congress went along, spend a sum equal to the value of all the goods and services produced by the 82 million people of Germany, the world’s fifth-largest economy. And in its modern form, a third part is dire prediction, a collection of uncomfortable, indisputable facts showing the unsustainable fiscal course the U.S. government is on.

The budget doesn’t record what might have been. . . . And for all its excruciating detail, the president’s budget doesn’t ultimately settle anything; the Constitution gives Congress the power to tax and spend. But neither is “presbud”—as it’s known to insiders on the congressional committees that decide how to spend taxpayers’ money—irrelevant. The budget is the starting point for an annual round of maneuvering that ranges from high-minded debate about national priorities and “hard choices” to big-money lobbying and small favors for home-state constituents. The details buried in it—which programs should live and which should die, which should get more and which should get less—often become law.

Ultimately, the federal government’s power comes in three forms: its physical force, both foreign and domestic; its ability to make and enforce rules that govern our lives; and its power to tax and spend. The budget—and this book—is about the third form. . . .

The president's budget is available online:

• Current budget: https://www.whitehouse.gov/omb/budget/
• Past budgets: https://www.govinfo.gov/app/collection/budget