Separation of powers under the United States Constitution:

Richard Nixon used national security as a basis for his expansion of power. He asserted, for example, that "the inherent power of the President to safeguard the security of the nation" authorized him to order a wiretap without a judge's warrant. Nixon also asserted that "executive privilege" shielded him from all legislative oversight; furthermore, he impounded federal funds (that is to say, he refused to spend money that Congress had appropriated for government programs). In the specific cases aforementioned, however, the Supreme Court ruled against Nixon. This was also because of an ongoing criminal investigation into the Watergate tapes, even though they acknowledged the general need for executive privilege. Since then, Nixon's successors have sometimes asserted that they may act in the interests of national security or that executive privilege shields them from Congressional oversight. Though such claims have in general been more limited than Nixon's, one may still conclude that the presidency's power has been greatly augmented since the eighteenth and nineteenth centuries.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Into which tapes was there an ongoing civil investigation?
unanswerable