Final answer:
Nixon's program of revenue sharing with localities is best characterized by the use of block grants, which provide states and local governments with greater flexibility than categorical grants.
Step-by-step explanation:
The money that flowed to localities as a result of Nixon's program of revenue sharing best characterizes the use of block grants. Unlike categorical grants, which have strict limitations and must be used for specific purposes with numerous conditions, block grants offer a more flexible approach allowing local governments to determine the best use of these funds based on their own priorities and needs. Richard Nixon started the revenue sharing program, but Ronald Reagan also significantly expanded its use during his presidency in the 1980s, aligning with his belief in the efficiency of state and local governments managing resources. However, the information provided also suggests that over time, block grants can become more restrictive as new administrative requirements are imposed - a process known as creeping categorization.