For the same reason, there was substantial resistance in Congress to the moves to take the transportation spending off budget. Thus, the compromise final version left it on budget but converted the outlays to a form of mandatory spending, instead of discretionary spending. Each SAP usually covers a single bill. SAPs are used to help position the White House on legislation that is likely to come to the president for signature. If the president is inclined to veto a bill, the SAP will give advance notice of these views.
SAPs use a distinct set of catch-phrases.
This approach gives the president some negotiating room. It's meant to meet funding needs that were unforeseen when the thirteen appropriations bills were passed. In fact, the president routinely sends supplemental spending requests to the Hill throughout the year. There is no limit, although there haven't been more than two supplemental spending bills in recent years. A CR is a device that keeps agencies of government funded even when there is no underlying appropriations act.