President Trump has always defied the laws of political gravity, seemingly impervious to setbacks that would sink any other figure and immune from the traditional ebb and flow of campaign cycles. But his capitulation in the fight over releasing the Epstein files, and other recent developments, suggest that, when it comes to Congress, the president is subject to at least some of the same currents as his predecessors, as the first signs of his lame duck status emerge. The willingness of congressional Republicans to defy Mr. Trump and back legislation requiring the disclosure of federal files on Jeffrey Epstein, the...