This subpoena has nothing to do with PRISM; it's really more of an effort to link the White House to the IRS targetting of conservative groups (which was apparently just an agent running amok).
Ultimately, though, there's the classic adage about the president: "The buck stops here." If Obama was aware of PRISM (which I have to believe he did), then he also had the choice of stopping it. The same is true of the IRS scandal. Even if he did not (unlike Nixon) direct the programs, knowing about them and not stopping them (again, if true; I really don't know) is tantamount to running them.
Ultimately, though, there's the classic adage about the president: "The buck stops here." If Obama was aware of PRISM (which I have to believe he did), then he also had the choice of stopping it. The same is true of the IRS scandal. Even if he did not (unlike Nixon) direct the programs, knowing about them and not stopping them (again, if true; I really don't know) is tantamount to running them.