What was the immediate reason that caused us secretary of state william jennings bryan to resign in june 1915?

William Jennings was the secretory of the state in 1915. He resigned because of the fear that President Wilson's stance against Germany would drag US in the war. The main reason for deteriorating of relations between the Germans and US was the sinking of British liner Lusitania by a German Submarine. So when the president tried to send a note to Berlin after this incident, Secretary of state Jennings resigned and denied from signing the note prepared by Wilson. He did so because he was afraid that Wilson's steps would draw US in the war.