This is a big, complicated, story that I’m going to try to tell as simply as possible.
One of the ways to conceivably save yourself during the Holocaust was to obtain some sort of protection from a foreign government. Meaning–if you were stateless, but got papers saying that you were under the protection of Chile (or were a Chilean citizen) you would be treated as a foreign national and kept in a civilian internment camp. This was usually much nicer than concentration camps and you could receive mail and relief packages.
One of the civilian internment camps in France was called Vittel. Americans and British caught in France were interned there, as well as Jews who had these papers identifying them as under foreign protection–mainly the protection of Latin American republics. At Vittel, there was an Orthodox group with Latin American papers.
In April 1944, members of the Orthodox community in New York found out that the Germans were rejecting the validity of these papers and were deporting a group of more than 200 Vittel internees, including the Orthodox group. The WRB knew about Vittel and back in February, had written a cable to Bern to ask the Swiss to let the Germans know that the US demanded the papers be considered valid. But the State Department never sent this cable, and never told the WRB that the message wasn’t transmitted.
On April 6th, a group of Orthodox rabbis came down from New York to plead with Morgenthau to intervene and prevent the deportation of the group from Vittel. There’s a LONG meeting about this. At the end of the day, the State Dept promises to send the cable to Bern. Morgenthau vows to stay in his office until they do. After finally getting a promise it was being transmitted, he went home late.