When is a Reuben sandwich not just a Reuben sandwich? When one eats it amidst a denizen of rabidly committed, frequently vitriolic, and unapologetically devoted Hillary Clinton supporters.

The scene at Harry's Pub in the Marriott Hotel, downstairs from the site of the Rules and Bylaws Committee hearing, was emblematic of the double-edged sword that has become the Democratic primary. One the one hand was the political...