According to the travel agent, what do a member of Lincoln’s cabinet, Ambrose Bierce, and Judge Crater all have in common?

The travel agent suggests that each of these people is in some way associated with the faraway utopia of Verna. He says that the unnamed member of Lincoln's cabinet is in fact from Verna. He was put in the cabinet during a period when the people of Verna were "simply observers," watching what was happening on planet Earth. When they began to take an active role in events on Earth (just before World War I broke out, according to the travel agent), they began to rescue people from the planet, which they are convinced is on the decline. The travel agent compares this practice to rescuing one's neighbors whose house has caught on fire. Verna is a happy place where people live long and carefree lives. Their work is fulfilling, and their relationships are genuine. It is held in stark contrast to the dreary life of Charley and other New Yorkers.
Ambrose Bierce is one of the people the Vernans "rescued," and the travel agent says that the famous author wrote several more books. Charley, the narrator, surmises that Judge Crater, a New York judge who famously disappeared without a trace in the midst of a scandal, may have gone to Verna, and the agent confirms that they had, in fact, been joined by a judge from New York. So what these three individuals have in common is that they are used by the travel agent to demonstrate the possibility of escape to Verna and a better life, a possibility that Charley unfortunately spurns out of his fears that the whole "Verna" story is a sort of scam.