That authority, known as executive privilege, isn't in the Constitution. It hasn't been clearly defined by the courts. Yet invoking it has proved effective for presidents determined to keep witnesses or documents away from congressional investigators.
President Barack Obama is the latest to assert the privilege.
He refused on Wednesday to turn over some Justice Department documents about a botched anti-smuggling operation that allowed hundreds of guns sold in Arizona to end up in Mexico. The House Government Oversight and Reform Committee has voted to hold Attorney General Eric Holder in contempt of Congress. The committee's recommendation goes to the full House for a vote, unless the White House and lawmakers negotiate a way to defuse the conflict.
A look, in question and answer form, at executive privilege and the fuzzy state of the law regarding showdowns between Congress and a president:
Q: How can a president shrug off a subpoena from a congressional committee?
A: Presidents say they should be free to engage in private decision-making with their advisers without fearing how their words or internal memos might look to Congress or the public. Several presidents have argued that this authority also extends to the work of high-level agency officials, even if they weren't communicating with the president or White House about that work.
Q: Where does the idea of executive privilege come from?
A: It's a principle based on the constitutionally mandated separation of powers — the idea that the executive branch, Congress and the courts operate independently of each other.
The concept of executive privilege dates at least to 1792, when Congress was probing St. Clair's Defeat, a disastrous battle against American Indians that cost the lives of hundreds of U.S. soldiers. Washington and his Cabinet decided the president had the right to refuse to turn over some documents if disclosing them would harm the public. In the end, Washington gave lawmakers what they sought. But the idea that later became known as executive privilege took root.
Q: Didn't the Supreme Court settle the issue when it ordered President Richard Nixon to hand over the Watergate tapes recorded in the White House?
A: Not really. The court ordered Nixon to surrender the tapes in that case — a criminal investigation. But the justices also found a constitutional basis for claims of executive privilege, leaving the door open for presidents to cite it in future clashes with Congress.
Q: Do presidents claim executive privilege often?
A: Most reach for it sparingly. Wednesday was Obama's first time in his 3 1/2 years in office. His predecessor, George W. Bush, cited it six times in eight years. Bush's father invoked it only once in his single term, to withhold a memo related to a Navy jet project canceled amid billions of dollars in cost overruns.
The administration of President Bill Clinton, who faced investigation of his Whitewater land deals and then impeachment in a sex-and-lies scandal, apparently asserted executive privilege 14 times. Those claims weren't put in writing, however, and some were quickly dropped.
Q: What comes next for Obama?
A: Probably more negotiation. In the past, presidents and lawmakers have been loath to let an executive privilege fight escalate into a court battle.
Q: Why not go to court to settle questions about executive privilege once and for all?
A: There's too much risk for both sides. Presidents worry that if they lose, courts will take away a valuable tool and weaken the power of the office. If the lawmakers lose, they could permanently weaken Congress' subpoena power when it investigates executive branch blunders.
Q: What if the White House and Congress can't reach a compromise?
A: The next step is a contempt of Congress vote in the full Republican-controlled House. Full House approval would send the case to the local U.S. attorney for enforcement. Who is that U.S. attorney's boss? Holder and, ultimately, Obama, who appointed him.
That's why the Justice Department traditionally declines to pursue such criminal contempt of Congress cases.
Q: Is there something else Congress could do?
A: If, as history suggests, the Justice Department won't prosecute a criminal case against Holder, the House could hire its own lawyer and file a civil lawsuit in federal court in hopes of winning an order for Holder to turn over the documents. But in addition to the risk of losing, a court fight would be long and drawn out, making that an unappealing option.
The Democratic-controlled House filed suit in 2008 to compel testimony from former aides to President George W. Bush. Lawmakers were investigating whether the firings of nine U.S. attorneys had been politically motivated. The House won the first round in court; while that decision was under appeal a settlement was reached and the lawsuit was dropped.
Lawmakers finally heard some of the testimony they had sought a year and a half earlier — but only after Bush's term had ended and a newly elected Congress had been seated.