That is the case with the NSA wiretap story. Evidently, this power had been recognized as Constitutional for the executive to monitor non-purely domestic communications:
In the Supreme Court's 1972 Keith decision holding that the president does not have inherent authority to order wiretapping without warrants to combat domestic threats, the court said explicitly that it was not questioning the president's authority to take such action in response to threats from abroad.
Four federal courts of appeal subsequently faced the issue squarely and held that the president has inherent authority to authorize wiretapping for foreign intelligence purposes without judicial warrant.
The only thing that really seems all that different in this case is that we know that this particular administration was using that authority. I leave it to your particular sense of cynicism as to whether you think that previous presidents did the same. I also leave it to you to decide if more of this might have helped prevent previous attacks, or if there were potential attacks that never happened because of this.
Link via Instapundit.