I don't know what the liberal answer is to "how to stop the genocide of innocent Palestinians". Who are the liberals here? Are they in power? If they are in power, voting probably isn't going to punish them because as I have said before, voting will only slow the decay.
Ideally we would have a voting system that would support more choices so we could actually "punish" a leader without pushing the US into fascism faster, but we aren't there yet.