Newsweek has an online interview with the always insightful Jonathan Sarna regarding Sharon, Israel, and their relationship with American Judaism. Sarna, as expected, is insightful and makes some excellent points but the inherent limitations of such an interview prohibit fully sophisticated answers.
For some examples, on describing the relationship between Sharon and the American Jewish population:

Here, a man [Sharon] who had so strongly advocated settling every inch of land, and was more responsible than anyone else for the settlements, was pulling Jews out of those settlements in an effort to create a viable Palestinian state and Israeli state. I think even those who disagreed had enormous respect for his ability to really change his position.

This this is a very nice thought, but I think it’s overly optimistic. Yes, it is noteworthy when people change their minds and in many cases it is commendable. However, when dealing with such incendiary issues such reversals are more often then not seen as betrayals, especially when someone is elected under those pretexts. (Think Bush nominating to the Supreme Court a judge from the 9th Circuit Court of Appeals). How such reversals are perceived is completely dependant on which side you happen to find yourself.
On the question “Is there a feeling among Jews in the United States that if you criticize the government of Israel, you’re criticizing Israel itself?” Sarna describes an evolution in popular thought:

But I think as time has gone on, it has become clear that the question is how one dissents. Certainly the Jewish community was not unanimously in support of the removal from Gaza. But I think it’s now well understood that American Jewry, where church and state are separated, [are] really unable to give unwavering support to a religious situation in Israel where religion is deeply enmeshed within the state.

This is a fascinating response as Sarna attributes political dissension to different ideologies of religion and politics. It is nearly impossible to discuss Israel without at some point addressing the religious impact,¹ but in the more secularized American society it is significantly easier to overlook or minimize religion’s real significance.
On the effect of Sharon’s absence on American Jews:

American Jews, in some ways, are going to feel lost with whoever succeeds Sharon. They don’t know the next generation of Israeli politicians, with the exception of [former prime minister Benjamin] Netanyahu. But he seems very unlikely at this point to take on the center. I think it’s going to take time before the American Jews get to know these people, and I think the same is true on the national scene.

Jewish Americans are probably familiar with only a handful of Israeli politicians. This is probably due to the fact that the same people keep running Israeli politics. Most of those old timers have long and well documented histories such that even the uninitiated can more easily catch up on their background and ideologies. But once you get to even the party leadership, things get a little murkier.
On the change of American Jewry’s opinion of Sharon:

Sharon was a man of very great personal charisma, and I think that many American Jews, even if they weren’t in love with his policy, came to believe that even though it may be difficult to watch settlements uprooted, this seemed like the most sensible policy.

Here Sarna is guilty of something many writers do – the ambiguous qualifier of “many.”² Still I think Sarna is correct considering the politically liberal political tendencies certainly among the religiously liberal Jewish communities. I will also suggest that the Rabin Factor probably discourages militant rhetoric from the right.
I’d recommend reading the whole article if nothing else to inspire some intelligent conversation.

1. On this point I highly recommend reading Arther Hertzberg’s The Fate of Zionism.
2. Yeah, I know.