This really isn't all that shocking or unprecedented.
When interest groups that want to cut Social Security and Medicare benefits, abolish the inheritance tax and make it easier to dump coal ash and fracking fluid in public waterways try to prevent people who oppose those things from getting elected, they don't say, "State Senator Smith's problem is that he wants you to have healthcare in retirement and have water that's safe to drink." They say, "State Senator Smith is a radical liberal elitist who wants to take away your guns, abort babies, and stand with those who kneel during the national anthem."
Israel/Palestine simply isn't a priority one way or another for the overwhelming majority of people, and the people for whom it is are not persuadable. So you focus on getting the politicians who agree with you on that issue elected or defeated via other means.