John Yoo explains for National Review Online readers why conservatives should be concerned about Barack Obama’s abuse of presidential power.

The Framers established an independent presidency because they wanted a branch of government that could move with “decision, activity, secrecy [and] dispatch,” in the words of Alexander Hamilton. They realized that only a single executive could protect the nation during emergencies and crises, which become particularly acute in foreign affairs and national security. George Washington, Abraham Lincoln, and Franklin Roosevelt became our greatest presidents because they brought the nation through the challenges of independence, civil war, and the existential threat of fascism. As the United States has expanded from a small collection of former colonies into a global power, the presidency has grown with it.

Mr. Obama has only shrunk from leadership in the circumstances where the Founders empowered him. When Syria crossed the “red line” by using chemical weapons in its civil war, he hid behind Congress and the United Nations to avoid a military response. He has stood by as Russia annexed Crimea and continues to destabilize Ukraine. He completely withdrew American forces from Iraq, with disastrous consequences, and he plans the same in Afghanistan. Even though he vigorously deploys drones and electronic surveillance against terrorists, Mr. Obama has imported judicial notions of due process to limit targeting, detention, and trial. And Mr. Obama risks the executive’s virtues for small political gains, such as his refusal to notify Congress about the prisoner swap of five Taliban leaders for Sergeant Bowe Bergdahl.

Mr. Obama’s true threat to the constitutional order arises at home, not abroad. He refuses to enforce the federal immigration laws to deport illegal aliens brought here as children. Although this is a worthy policy goal, embodied in the proposed Dream Act, the White House has no discretion to ignore laws except when they violate the Constitution. Likewise, the administration has delayed the timetable for insurance policies to meet Obamacare requirements, freed some employers from its demands, and approved health-care plans that do not meet the statute.

Mr. Obama has reversed the polarity of the presidency by exercising unilateral constitutional powers over domestic, rather than foreign, affairs.