An emotional Attorney General Merrick B. Garland addressed new citizens on Saturday at Ellis Island, the site of his family’s American origin story, and warned that the country had become dangerously divided by political factionalism, which has imperiled the democracy and the rule of law. Mr. Garland was presiding over the oath of allegiance for 250 naturalized citizens at the iconic immigration processing center, on the anniversary of the signing of the Constitution in 1787. As the new Americans rose to recognize their home countries — about 60 of them, with origins from Albania to Yemen — he told them...