Electoral politics ends with the presidency. It doesn’t start there. Bernie worked for progressive causes for decades before running in 2016. He worked his way up from mayor to Congress to Senate. His near miss in the primary in 2020 pulled Biden to the left on several issues.
If you want to end support for Israel, and I agree we should end support for Israel, even if they stop the war tomorrow. Then you should be writing letters, going to county Democratic meetings and finding candidates to run for state legislature that share your beliefs.
They are just declaring their neighbors illegitimate and marching in like Putin.