The Jewish diaspora is a unique phenomenon exacerbated by the Holocaust of World War II. Jewish-American identity is unique because of the laws of the country as compared to other places. Plus the USA isn't a quasi-religious state like Israel. Jews are an ethnic minority in America, yet somehow they manage to be a vocal minority which speaks out in favor of US-Israel relations every election cycle.
I think that American Jews have a different identity from Israeli Jews because of their cultural experience. Most Jews living in Israel live under a greater shadow of terrorism than American Jews do. At the same time, since Israel is predominantly Jewish, the religion is part of every aspect of life in Israel, not simply religious life. This is not true for American Jews.
Here in America we accept all races and religions, so the American people will be accepting of the Jews, and will side with them if some other country is trying to harm them or take away their lands. We have formed a relationship with the jewish that will force us to help them.
Yes, the history of Jews in the United States has created a unique Jewish-American identity separate from that formed in Israel. I have many Jewish friends who have been either disillusioned or enlightened upon spending some time in Israel. Apparently it's a bit of a culture shock at realizing how conservative their religion is outside of North America.
I believe the current generation of the Jewish population in the United States has probably created a unique Jewish-American identity that is separate or far removed from that formed in Israel. It's hard to say as someone not associated directly, but I find it hard to believe that they could have similar identities given the vast differences.