Congress's role in Iran nuclear deal shows limits of Obama's power

The fight over whether Congress should be able to block any nuclear agreement with Iran was one more chapter in a fundamental struggle between the executive and legislative branches since the beginning of the republic. Over two centuries, presidents have increasingly played a larger role in shaping national and foreign affairs. Bill Clinton went to war in Kosovo without explicit congressional approval. George W. Bush negotiated an agreement for troops to stay in Iraq without a vote by lawmakers.

In Mr. Obama’s case, the use of executive power has come to define his final years in office now that he has, in many instances, given up on working with what he considers to be recalcitrant Republicans who captured the House in 2010 and the Senate in 2014. Republicans argue that he has abused his power, and they saw the Iran bill as a victory in balancing the scales.

“This is perhaps a high point of challenging the White House’s undisputed judgment on these matters,” said Thomas Karako, a senior fellow at the Center for Strategic and International Studies, who has written on executive power in foreign policy. “But this is just the latest wrinkle in a many-decades-long struggle between the president and the Congress.”