Within the confines of the law, your best chance at pressuring Harris to change her position is to very vocally demand the Democrats cease support of Israel immediately, and that if they don’t then you will not support or vote for them. What other leverage do you have over them?

Harris is sitting here telling you that she will not stop funding/supplying the genocide of Palestinians, that she will take a stricter border policy and continue building the wall, that under her the US military will be the most lethal fighting force. Not to mention her horrific track record up to this point. A vote for Harris is just as much a vote for fascism as a vote for Trump is. Not that voting out fascism in the USA was ever a realistic option to begin with.