Its all the non-Israeli Jewish US citizens who naturally tend to be sympathetic to Israeli interests. This has lately been reinforced by a huge right-wing, fundamentalist Christian constituency who have abandoned their usual anti-Semitism and suddenly become rabidly pro-Israel because it feeds into their apocalyptic fantasies, reactionary paranoia and anti-Muslim bigotry.

Don't get me wrong, I'm certainly pro-Israel in my politics and sympathies, (just look at their enemies!) but not so much that I choose to ignore the pro-Israel lobby and the very persuasive pro-Israeli propaganda machine that operates almost unopposed in the USA. We weren't always so totally pro-Israel, we did not back them during Suez, and our shift in policy evolved along with American public opinion. There's more public relations than public policy behind that shift. And Israel, although the only true liberal democracy in the Middle East, also has its share of questionable policies and practices when dealing with its own history (ancient and recent) and neighbors.

As always, the truth is never one-sided. You just have to study both sides and then pick the lesser of two evils.