The US Govt wanted badly to join WW2 but public support wasn't there.
the Mcollum Memo outlines how support could be fostered and the Stimson Diary demonstrates they were aware of a pending attack.
October 7 1940 McCollum Memo:
It is not believed that in the present state of political opinion the United States government is capable of declaring war against Japan without more ado; and it is barely possible that vigorous action on our part might lead the Japanese to modify their attitude. Therefore the following course of action is suggested:
A. Make an arrangement with Britain for the use of British bases in the Pacific, particularly Singapore
B. Make an arrangement with the Netherlands for the use of base facilities and acquisition of supplies in the Dutch East Indies
C. Give all possible aid to the Chinese government of Chiang-Kai-Shek
D. Send a division of long range heavy cruisers to the Orient, Philippines, or Singapore
E. Send two divisions of submarines to the Orient
F. Keep the main strength of the U.S. fleet now in the Pacific[,] in the vicinity of the Hawaiian Islands
G. Insist that the Dutch refuse to grant Japanese demands for undue economic concessions, particularly oil
H. Completely embargo all U.S. trade with Japan, in collaboration with a similar embargo imposed by the British Empire
If by these means Japan could be led to commit an overt act of war, so much the better. At all events we must be fully prepared to accept the threat of war.
12 Days before the attack on Pearl Harbor, Secretary of War, Henry Stimson wrote in his journal:
"(Roosevelt) brought up the event that we were likely to be attacked Monday, for the Japanese are notorious for making an attack without warning, and the question was how we should maneuver them into the position of firing the first shot without allowing too much danger to ourselves. It was a difficult proposition.”
https://www.jstor.org/stable/1897543
