based upon common law rather than separation of powers, and its history traces back to the English crown privilege (now known as public-interest immunity). In contrast, the presidential communications privilege is another specific instance of executive privilege, usually considered based upon the separation of powers. Therefore, it is more difficult to overcome than the deliberative process privilege. A significant requirement of the presidential communications privilege is that it can only protect communications sent or received by the president or his immediate advisors. In contrast, the deliberative process privilege may extend further down the chain of command. In the context of privilege assertions by United States presidents, law professor Michael Dorf has written: "In 1796, President George Washington refused to comply with a request by the House of Representatives for documents related to the negotiation of the then-recently adopted Jay Treaty with the Kingdom of Great Britain. Washington reasoned that the Senate alone plays a role in the ratification of treaties, and therefore the House had no legitimate claim to the material. Therefore, Washington provided the documents to the Senate but not the House." President Thomas Jefferson continued the precedent for this in the trial of Aaron Burr for treason in 1809. Burr asked the court to issue a subpoena duces tecum to compel Jefferson to testify or provide his private letters concerning Burr. Chief Justice John Marshall, a strong proponent of the powers of the federal government but also a political opponent of Jefferson, ruled that the Sixth Amendment to the Constitution, which allows for these sorts of court orders for criminal defendants, did not provide any exception for the president. As for Jefferson's claim that disclosure of the document would imperil public safety, Marshall held that the court, not the president, would be the judge of that. Jefferson refused to testify personally but provided selected letters. In 1833, President Andrew Jackson cited executive privilege when Senator Henry Clay demanded that he produce documents concerning statements the president made to his cabinet about the removal of federal deposits from the Second Bank of the United States during the Bank War. Cold War era During 1947–49, several major security cases became known to Congress. There followed a series of investigations, culminating in the famous Hiss–Chambers case of 1948. At that point, the Truman Administration issued a sweeping secrecy order blocking congressional efforts from FBI and other executive data on security problems.