Some would say that the failure is explained by the fact that Jews are Americans and they've got a lot of other issues that matter to them beside Israel. Which is, of course, true. And needless to say, moonbat wailing to the contrary notwithstanding, the Democratic party is also extremely pro-Israel in its policies.
But the nature of GOP support for Israel is simply not aimed at or shaped by the support of Jewish voters. It's support is aimed at a vastly larger evangelical Christian constituency. And the aims, mores, values, etc. of each group are profoundly different. (The most obvious difference is that American Jews tend to support Israel because of a mix of nationalism, ethnic identification, religious belief and democratic values while the religious right tends to support Israel because its existence will hasten the apocalypse when God will vanquish the Jews en masse in hellfire and turn Israel into a vast evangelical theme park. So the two groups sort of come at the issue from different perspectives.)
At one level, this is obvious: we know the religious right is a huge constituency for uber-hawk policies on Israel. But I'm not sure we think through its implications as clearly or as deeply as we might.