If you can get past antisemitic conspiracy theories about AIPAC you'll find out it's a group of Jewish American citizens and they have exactly as much right to representation as you do. There are a lot of people in the pro-Palestinian movement that are in this "uncommitted" movement which is an attempt to threaten politicians with removal from office if they don't change foreign policy to help their side in a foreign conflict. How is what the pro-Palestinian movement is trying to do any different from what AIPAC does? The only difference is AIPAC is significantly more competent at doing what the pro-Palestinian movement is trying to do. Also the pro-Palestinian movement has an antisemitism problem that they're in denial of which means they're doing nothing to address. So it's obvious to any politician which of these groups they'll be happy to associate with and which group they'll generally avoid. The pro-Palestinian movement has to fix their problems to be able to have any kind of influence.

Third parties are simply not viable in the current system. There is a proposal to have ranked choice voting at least for congress, but it's currently lacking the votes needed to pass. That would make third parties at least possible in congress. I'll give you one guess about which party has proposed it.