The power to keep executive communications confidential, especially as they relate to national security. Here's a fabulous resource from the Miller Center on presidents' views on executive privilege.
Sentence
Presidents can claim executive privilege to withhold documents or to prevent members of the executive branch from testifying in order to protect their communications. The reasoning goes that the president’s advisers must be able to offer advice freely and without fear of censure. But that doesn’t always hold up in court — just ask Richard Nixon, whose attempts to withhold audiotaped recordings connected to the Watergate scandal were blocked by the Supreme Court. Or Bill Clinton, who tried to dodge testimony about Monica Lewinsky and was overruled by the courts.
