At Foreign Policy, James Goldgeier and Elizabeth N. Saunders explain that legislators have become less and less interested and conversant in the details of foreign policy and national security.

Why this decrease? The rise of partisanship is one important reason. Although foreign policy has never been fully isolated from politics, political polarization began to rise in the 1970s, and it increased sharply in the 1990s. Today, members of Congress reflexively support their own party. In periods of unified government, this means extreme deference to the president. In periods of divided government, it means congressional gridlock. Neither scenario yields much in terms of congressional oversight.

Polarization also gives presidents reason to simply ignore Congress when making foreign policy. As the political scientist Kenneth Schultz has argued, with members less willing to cross the aisle, it is “more difficult to get bipartisan support for ambitious or risky undertakings, particularly the use of military force and the conclusion of treaties.” And so presidents opt for alternatives such as executive agreements over formal mechanisms such as ratified treaties