YOU SPELLED TRAITOR WRONG: The Wall Street Journal editors on “President Guantanamo.”

President Obama rode into the White House vilifying George W. Bush’s “unchecked presidential power” and “ignoring the law when it is inconvenient,” as he put it in 2007. Yet now Mr. Obama is poised to exceed any executive action his predecessor so much as contemplated as he may shut down Guantanamo Bay in defiance of inconvenient laws he signed. . . .

With the end of his tenure in sight, the President is now looking for legal excuses to close the prison without Congressional approval. Since the KSM fiasco in 2009, Congresses run by Democrats and Republicans have specified in defense bills that no Treasury money may be used to transfer or maintain detainees to the U.S. The prohibitions in the most recent defense legislation—which passed the Senate 91-3 and the House 370-58—are the strongest ever.

Yet the Pentagon may soon announce a plan to transfer the remaining 107 dangerous combatants that no other country will accept to a domestic facility such as Fort Leavenworth or the Colorado supermax. Amid Mr. Obama’s many executive rewrites on carbon, ObamaCare and labor this flouting of the law would be the worst.

Mr. Obama’s legal surrogates including former White House counsel Gregory Craig now argue that Congress’s spending restrictions are unconstitutional. They claim the executive has exclusive Article II powers as Commander in Chief over the tactical conduct of war and diplomacy, including the custody of detainees.

But control over wartime prisoners is divided between the President and legislature. The Constitution vests Congress with the power to “make Rules concerning Captures on Land and Water,” and not even the most zealous unitary executive theorists read the Captures Clause out of Article I. Congress cannot micromanage military operations, but it has a constitutional role in regulating them.

In 2009 Office of Legal Counsel chief Steven Bradbury wrote an opinion disavowing the legal argument Mr. Craig is now promoting, and Mr. Obama has abided by Congress’s restrictions for seven years. No current emergency justifies ignoring Congress, as Mr. Obama claimed when he traded five Taliban for Bowe Bergdahl in violation of a prisoner swap law.

With this President, it’s not the Constitution that defines his power; it’s what he can get away with.