How did FDR use his words to encourage public support for U. S. involvement in WWII?""

HE told Americans that they needed to discourage invasion and prepare for future attacks

Explanation:

American isolation policy which states that The United states of America will remain neutral in Future wars which are not directly involving The U. S i. e war fought on foreign soil. but President Franklin D Roosevelt needed to aid France and Britain due to the facts that they were Allies to America but the Isolation policy prevented him from doing so.

In order to encourage public support for his Moves he had to cite several reasons in his speech that would encourage public support, one of such was the citation of the bombing of the pearl harbor by the Japanese and the need for Americans to prepare and test themselves against future attacks from enemies.