“The next president of the United States will only be the president of a party,” Thomas Jefferson predicted as George Washington, with his singular stature, ceded the office. In the modern era, that cramped vision of the presidency has never been as starkly on display as it was on March 4th, when Donald Trump addressed a joint session of Congress for the first time in his second term. At least within the chamber that evening, he was the president of worshipful Republicans, and the scowling, leaderless Democrats seemed relevant only as his foil.