Apresident without a vice president is like a captain without a first mate, but some U.S. presidents — four, to be precise — have nevertheless had to serve without one. They were John Tyler (1841-1845), Millard Fillmore (1850-1853), Andrew Johnson (1865-1869), and Chester A. Arthur (1881-1885), all of whom ascended to the presidency when their predecessors died in office. Because the 25th Amendment didn’t lay out an official process for naming a new VP in such an event until 1967, those four commanders in chief simply went without one. All four failed to win reelection; some even failed to secure...