Kevin Drum points to several conservative commentators accusing American Jews of, among other things, being "downright stupid" for being Democrats. The reason is because right now we have a Republican President who is incredibly pro-Israel. Both Ezra Klein and Matthew Yglesias point out that such a claim makes it then difficult to condemn the statements by some that Jews have "dual loyalties" divided between America and Israel. That's true, but (speaking as one of the idiots) I'd like to add a few thoughts of my own.
First of all, even if the GOP is slightly more pro-Israel than the Democratic party, it's not by any meaningful amount. There was, what, around 10 votes against the last resolution supporting Israel in its conflict against Hezbollah? In America today, both parties are strong on Israel, so from my perspective it is effectively a wash, and any advantage the GOP has is negligible. And of course, I don't think it's unreasonable to say that Israel is disadvantaged by poor foreign policy decisions and misadventures elsewhere in the Middle East. Stirring up instability there means bad things happen to Israel.
Second, it's arguable (indeed, I think it's evident) that the reason that the Democratic party is so strong on Israel is because of its strong, consistent Jewish base. Remember, Jews are matched only by Blacks in terms of party loyalty. I think we've done a good job keeping the Dems in line on the issue. Contrast that to Europe, where Jews are far less politically influential and Israel (and Jews themselves) are time and again kicked to the curb by both the left and the right. I'm not saying that Democrats only defend Israel because its politically expedient, but I am saying that a mass exodus would significantly strengthen the hand of the McKinney wing of the party and probably result in a net weakening of support for Israel in the body politic.
Third, and not to be obvious, there are a lot of issues besides Israel that are important to Jewish voters. Democrats have the advantage on nearly all of them. On abortion, social justice, church/state (that's a huge one), economic justice, and civil rights, Democrats are far more in tune with Jewish positions than are Republicans. It's not even close.
There are Democrats who take positions on Israel I find objectionable. Frankly, that's what primary battles are for, and as Representative McKinney is about to find out (again), more Democratic voters than not won't stand for constant, single-minded Israel bashing. But by and large, I feel I'm giving up little, if anything, for Israel by my Democratic affiliation. And in terms of the issues that matter to my faith, I'm gaining a lot more.