Do you honestly believe that it's fair to say that the United States "allows anti-Semitism to thrive"? We are a free country where the state does everything it can to discourage racial and ethnic hatred. We have a Constitution which explicitly protects freedom of religion and laws against hate crimes which punish more harshly when the attempt is to intimidate an entire group of people. And since the Civil Rights era, our ideals of pluralism and tolerance of ethnic/religious differences in this country have enjoyed strong and growing popular support.
Surely you're aware of where this country came from in terms of anti-Semitism. Prior to World War II we were rolling in it. Since then it has become such a scurrilous charge that a major television network just suspended a *black woman* in the midst of a so-called "reckoning" against anti-black racism for expressing a mistaken (yet no doubt commonly held) notion about Jewry not constituting a race (at least in the context of the Haulocaust).
In fact, since (I'm assuming) you're sympathetic to the "wokeness" skepticism that motivates forums like this (as am I) consider how, in the post-WWII era, American Jews enjoyed such a strong cultural aversion to anti-Semitism so as to impose a largely bipartisan stigma against criticism of Israel - one that has only recently shown some signs of eroding. This stigma has been, in many ways, quite similar to woke anti-racism, refusing to brook any criticism of Israel with the slightest whiff of anti-Jewish tropes - which tend to involve themes of money, power, and influence. Surely you see the problem here.
I don't blame you for abandoning a political party; personally I think they're poison. But as the recent Whoopi Goldberg incident illustrates, greater willingness to criticize Israel, however misguided it may be, does not translate into greater anti-Semitism. And healthier political discourse demands that we learn to distinguish the two better than we have in the past. That is the downside to having an ethnic democracy (which one could be forgiven for seeing a sectarian state) claiming to represent the world Jewish diaspora.
Actual anti-Semitism on the fringe of the American left is nothing new. Around the turn of the century, many of us were gobsmacked at how some in the Black civil rights movement expected us to take Lewis Farrakhan seriously as a leader. And it is certainly nothing new on the fringe of the American right, where white Christian nationalism has festered out of sight of the American mainstream.
The history of countries which have promoted anti-Semitism is indeed awful. The history of countries that have permitted it in any way is impossible to generalize, because it includes virtually every nation where Jews have ever lived - there is even anti-Semitism in Israel! But few countries can say they've done a better job of stigmatizing it than America. And there is a reason that American Jewry has long leaned to the left politically - because of an understanding of the importance of civil rights, free expression, and opposing discrimination. The existence of some pro-Palestinian bias in geopolitics is a natural outgrowth of that, and should be of no more concern than people on the right babbling conspiracies about "Jewish space lasers" or equating COVID vaccine proponents with Nazi scientists.