Harry Enten digs into polling on the subject:
[T]here is a relatively wide difference between how Democrats and Republicans view Israel. Per the CNN/ORC poll, which mirrors other recent data, 51% of Democrats sympathize mostly with the Israelis, and 16% with the Palestinians, in the conflict at large. This compares to an 80% v 5% split between Israelis and Palestinians respectively among Republicans.
You might be wondering how there could be a 29-point split between Democrats and Republicans on pro-Israel sympathy, in contrast to only an 11-point difference between Democrats and Republicans on pro-Palestinian sympathy. That is chiefly because Democrats are far more likely to say their sympathies are with both Israelis and Palestinians (6%) or neither (14%). Put another way, Democrats aren't really any more sympathetic to the Palestinians than Republicans are, so much as they sympathize with both sides or don't care much for either.
The Dish 