What events move americans from isolationism to support for the war?

Pearl Harbor attack put an end to years of discussion and debate, the U.S. government and its people were united to go to war.

On December 7th 1941, Japan attacked by surprise an U.S. naval base near Honolulu, Hawaii. The Japanese fighter planes destroyed or damaged nearly 20 American naval vessels and over 3000 airplanes. They killed over 2,400 americans and wounded over 1,000. One day after the attack, President Franklin D. Roosevelt asked the Congress to declare war to Japan. On December 8th, 1941 the Congress approved the declaration. As a result, three days later, Germany and Italy, Japan's allies declared the war against the U.S.

The U.S. declared war to them oficially entering the WWII.