If those US Citizens were part of an "association" (as defined), such as Al Quada, the law makes it clear that they could be wire-taped.
This works just like the RICO (racketering) wiretaps that have been used for 30 years, signed by JohnFKennedy.
Just like you don't have to get a warrant for individual mobster; you don't have to get a warrant for every terrorists group member.
Period.
No, it doesn't. As much as you would like to believe it, a person does not stop being a US person because they are part of an association. Read this part carefully:
(B) there is no substantial likelihood that the surveillance will acquire the contents of any communication TO WHICH A UNITED STATES PERSON IS A PARTY; and
If a United States person is a party, at all, it means you cannot get a warentless wiretap. That is the LAW. I have cited it repeatedly. There is no part of the law that reads "Except in cases when that person is part of an association." If there is, please post it.