Sen. Rand Paul (R-Ky.) has quite rightly called on the Obama administration to publicly disclose its legal justifications for the claimed power to order the killing, without trial or hearing, of U.S. citizens abroad who are suspected of being terrorist leaders planning attacks against the United States. The dispute came up, most recently, in the context of David Barron's successful nomination to a seat on the U.S. Court of Appeals for the First Circuit. As a lawyer in the Office of Legal Counsel, Barron reportedly co-authored at least two memos providing the legal rationale for the administration's decision to order the killing of Anwar al-Awlaki, a U.S. citizen and propagandist for Al Qaeda in the Arabian Peninsula (AQAP).

Jennifer Rubin incorrectly accused Sen. Paul of "misunderstand[ing] the Constitution" which, in Rubin's view, "affords the executive branch replete powers in the foreign policy realm." Quoting John Yoo, Rubin suggests that Sen. Paul's approach would "[include] terrorists among those afforded constitutional protections."

Al-Awlaki was no saint, and that can make the issue seem trickier than it is. But calm evaluation of some basic facts make it clear that Paul is right to insist that the Obama administration explain its rationale (especially before Barron is confirmed to a lifetime position on a federal appellate court), and Rubin is wrong to suggest that Paul is defending terrorists.

These are the facts that matter, and show why Rubin's criticism is misplaced. First, although al-Awlaki was clearly a propagandist for AQAP, that is not why the Obama administration placed him on a kill or capture list (meaning that he could be killed if capture was not feasible). The administration claimed that al-Awlaki was a senior leader in AQAP involved in planning attacks against the United States that posed an imminent threat. This claim has never been proven. The Supreme Court has made clear that due process requires a meaningful hearing before a neutral decisionmaker before a U.S. citizen can be imprisoned, let alone killed. How, then, can the administration justify al-Awlaki's killing without hearing or trial?

The argument seems to depend on an implausibly twisted definition of due process. Attorney General Eric Holder claims that due process need not be judicial process—in other words, due process can be satisfied by a purely internal review within the executive branch, with no judicial oversight and limited congressional involvement. As Harvard Law professor Noah Feldman points out, this is an unprecedented definition of due process. As the Supreme Court explained in the 2004 Hamdi decision, due process plays an essential role in separation of powers, preventing the concentration of power in one branch of government (here, the executive branch). Holder's definition turns due process on its head. It is essential for the public to know whether the administration relied on something like Holder's approach in the Barron memos written to justify al-Awlaki's killing.

This helps expose the bankruptcy of Rubin's claim that the executive branch has "replete powers" in the area of foreign policy. Not so.

The framers of the Constitution quite consciously broke with the then-prevailing British model, which did assign plenary or essentially complete power over foreign affairs to the monarch. The framers, of course, were creating a republic, not a monarchy. The Constitution they drafted divided foreign affairs powers between the President and Congress. The President is Commander in Chief, but Congress has the power, for example, to declare war, to regulate commerce with foreign nations, define offenses against the laws of nations, and ratify treaties in the Senate. It is true that there is a long-standing myth that the President has plenary control over foreign affairs.

This myth has what seems to be solid support in the Supreme Court's 1936 Curtiss-Wright decision, which describes the President as the "sole organ" of foreign policy, citing a speech John Marshall gave in 1800 that used that term. But Marshall never went as far as the Court suggested. He described the President as the sole organ of the United States in carrying out treaties duly enacted by the Senate, not as the sole organ in the sense of possessing plenary or "replete" power over foreign affairs.

Even if Marshall had said this, he would have been wrong. The Constitution does not, in fact, assign the President control over foreign affairs. Rubin's casual reference to "replete" executive power in this area is sloppy and dangerous. The President, like Congress and the courts, does not possess unlimited power. Presidential power over foreign affairs is shared with Congress and, to some extent, with the courts (in the sense that they may exercise judicial review over some acts). Checks and balances cannot be swept aside so easily. It is Rubin, not Paul, who misunderstands the Constitution if she believes the President may always act unilaterally when it comes to foreign affairs. Outside of the emergency context (which was not, it appears, claimed by the administration here), such power simply does not exist.

Although Rubin suggests otherwise, Paul's criticism of the targeted killing program and his insistence that the Obama administration make the Barron memos available to the public has nothing to do with defending terrorists. To the contrary, he is rightly standing up for the principle that secret law has no place in a constitutional democracy, and that even U.S. citizens like al-Awlaki who are clearly no angels cannot be killed on the basis of unproven claims.

Below, see author Chris Edelson discuss presidential power with Reason's Nick Gillespie.