The American Congress reviews each of these programs, especially the bigger ones, the ones involving the most money, of course. The U.S. Congress reviews that. If they approve of it, they authorize the program in the authorization committees. And then in a separate set of committees called the appropriations committees, they actually appropriate the dollars for obligation, for expenditure.
So there is actually a double review: first in an authorization committee and then later in an appropriations committee. Those committees themselves have oversight and investigative staff who will also look at these programs, sometimes in great detail.