The big gains made by Palestinian parties in Israel’s general election pose an urgent and fundamental challenge to the country’s mainstream opposition: either cooperate with Arab Israelis or hand Benjamin Netanyahu a roadmap to political survival.

In the wake of Tuesday’s exit polls , the leader of the opposition bloc, Gadi Eisenkot, declared them a victory for “Israel’s Zionist national majority” but the real outcome looks as if it will be far more complex than that.

The greatest change between the new Knesset and the old will be the dramatically increased representation of Palestinian parties, which are projected to win 17 to 18 seats, up from 10. That redraws the battle lines on Israel’s political landscape.…