Typically someone in Congress or the President proposes a thrust to address a problem or new pursuit.
Congress passes legislation to effect that thrust and allocates taxpayer money to pursue it. The president signs off on that legialation.
The pursuit of the thrust is implemented via a program run by a bureau. This bureau has a head who hires staff who flesh out all the details of the program.
Unless the legislation is very specific about the goal of the thrust as well as a Performance Measurement the bureau charged with fulfillment has considerable latitude to determine the scope of the thrust and as a result the PerformanceMeasurement