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 personally testify but provided selected letters.