These documents are often compared to the warrants the government ordinarily needs for searches of Americans. But they're dramatically different from a conventional search warrant. A warrant is supposed to "particularly" describe who will be targeted by a search. It will typically include a suspect's name, as well as the address to be searched or the phone number to be wiretapped.
The documents released by the Guardian don't look like that at all. The first document is nine pages long and explains in some detail the factors the NSA uses to determine whether a potential surveillance target is a "US person"—if the answer is yes, then the agency cancels the planned surveillance. The second document, also nine pages, describes what the NSA does if it accidentally collects the private communications of Americans.
These documents look more like legislation than search warrants. They define legal concepts, describe legal standards to be applied and specify procedures for NSA officials to follow. For example, the second document states that "a person known to be an alien admitted for permanent residence loses status as a United States person if the person leaves the united States and is not in compliance with 8 USC § 1203 enabling re-entry into the United States."
But rather than being drafted, debated and enacted by Congress, the documents were drafted by Obama administration lawyers and reviewed by the FISC.
Congress is much better equipped than the courts to review this kind of quasi-legislative proposal. It has thousands of staffers and can spend months debating the details of a proposal. Members have the power to call witnesses and to amend legislation if it's not to their liking. And they debate in public, giving academics, public interest groups and members of the general public an opportunity to point out flaws and suggest improvements.
In contrast, the FISC has only 11 members and a limited staff. In most cases it hears testimony only from the government, and only in secret. It must make decisions within 30 days. In principle it has the power to modify proposed orders, but it lacks the manpower and expertise to exercise this power effectively. The FISC's secretive review process leaves no meaningful opportunities for third parties to point out flaws in the government's proposal and suggest alternatives.
And once the courts sign off on these general targeting procedures, no one outside the executive branch performs the function traditionally performed by the courts: double-checking that the government actually follows the rules. The government has some internal oversight mechanisms, but no one in the judicial branch verifies that the individuals the government targets for surveillance are actual foreigners, as the law requires.
The Constitution specifies that Congress should write laws and that the courts should interpret them. The founders set things up that way for a reason. Allowing the executive branch to effectively write its own rules, get them rubber-stamped by a secretive court and then comply with them on an honor system is guaranteed to produce rules that are more favorable to the government and less carefully drafted than rules drafted the old-fashioned way.