Before the bombing of Pearl Harbor in 1941, the United States was divided over whether or not to assist the allied countries in World War II. Because of the Neutrality Acts we were limited in how we could help supply other countries in their fight against the Axis powers.
President Roosevelt realized that at some point the United States was going to have to become involved, and he wanted to help other countries in their fight. When Britain began to run out of money to pay for materiel from us, he came up with the Lend-Lease plan. This plan, begun in early 1941 before our entry into the war, helped us supply Britain and other countries without violating the Neutrality Acts.
The United States also implemented an oil embargo against Japan to try to stop or slow down their military expansion in Asia. Believe it or not, Japan at this time got about 80% of its oil from America. This may have slowed Japan down, but it also backed them into a corner. They felt they had to attack our fleet at Pearl Harbor to give themselves a chance to secure more resources by force in Asia.
I have a relative, who wears baseball caps with labels like "The Gipper" or "The Big Stick," which are nicknames for American aircraft carriers, Roosevelt and Reagan. When I asked for the meaning for the cryptic labels, he said, "Girly, thems four and one-half acres of prime American real estate.”
To me that statement was just a cryptic as the nicknames, but on further questioning, he explained that it refers to the area of a super carrier's the flight deck.
So the point is that my relative is a bit of nerd, but he is expert on naval trivia.
He says that in the two decades prior to World War II, the United States navy’s burglars stole Japanese code books, which allowed them to read the Japanese government’s coded messages. In other versions of the story, the FBI stole the code books.
I doubt that Roosevelt knew about the decoded messages, but much of it happened during his administration, so it could be an answer to the question. Here is a website with one version of the story.