This question has two very distinct answers. Let us get the simple answer out of the way first. There are a great number of Americans who would never turn against Israel. Many, possibly a majority, of these people are Evangelical Christians. There are also a number of other Christians and traditional American patriots who also support Israel and whose support is virtually unshakeable. There is also a core of Jews, the majority being very religious but includes a sizeable number of Jews who are more Zionist than religious, who will support Israel through thick and thin. There are a small group of very religious Jews who are opposed to Israel for reasons of religious interpretation who would probably support Israel if there were to be a war against the Jewish state if only because of the numbers of Jews who would be endangered. What is surprising is that there exists a number of irreligious Jews who, other than any family members if even them, have no attachment to Israel and should Israel be on the wrong side of their political beliefs, then Israel would be cast aside as irrelevant and possibly seen as evil for opposing their politics. Finally, there some assimilated Jews who are in the far activist left who are fully supportive of the Palestinian Arab narrative and see Israel as the central evil in the modern world. These particular Jews politically are completely consistent with the beliefs of their non-Jewish extreme left travelers. These extreme leftists are mostly found within the Democrat Party as well as the Green Party, American Communist Party and some even in the Libertarian Party. Those extreme leftists who are not members of the Democrat Party would cross party lines to support an extreme leftist candidate from the Democrat Party. This is true for any electoral position from Dog Catcher to President of the United States and every position in-between. This would most definitely include city and county positions through state and include both houses of Congress.
Looking at the last Democrat Party fight over gaining the Party’s choice as Presidential candidate to run against Donald Trump, we saw an interesting fight which became very close and was only decided for Hillary Clinton, the centrist candidate, over Bernie Sanders, the extreme leftist candidate, where Bernie was supported very strongly by the youth from High School seniors and college youth as well as recent graduates under the age of thirty-five or as high as forty-five. These are the recent products of the education system which has become more of a regime of instructing the young on what to think and away from the teaching of how to think. Their math and science teaching has been simplified and even gone to an extreme where every answer will be considered correct as long as you can explain how you reached that answer to the mathematic problem. One of the methods taught now for solving algebraic problems is to guess and continue testing numbers until you find one that works, and that is it. So if the problem is basic as what does X equal if 1+2=X? If you claim that the answer is 4 and when asked why you explain that 1 and + equals 2 and with 2 you get 4, then you would get credit because you explained the way you reached the answer of 4 by assigning + to mean add another 1. The science is not the worst of the education currently being provided in the public schools. They offer no requirement for a civics course or any course which describes the government, how it was described in the Constitution. There is no requirement of American or World History. If you do take a history course it largely will cover the accomplishments of people who were minorities. Here is a simple example from over a decade ago. When my youngest child was attending a newly built school, the students were asked to present names of minority people and one child presented the name of Supreme Court Justice Louis Brandeis, the first Jew appointed to the Supreme Court. The child had that entry rejected because Jews are not a minority. They named the school after Roberto Clemente who played for the Pittsburgh Pirates, but the school was not even in Pennsylvania. Personally, I find Roberto Clemente as a fine choice as he was an exemplary man both on and off the field of play who was taken from us far too young.
These educational systems new directive of producing little drone humans whose political viewpoints are aligned with the system directive of supporting everything being centered around groups. They no longer give homework and many classes do not have textbooks but instead they work off handouts which the children are required to return to the teacher such that they are never taken home. All projects are assigned for groups to produce the assignment and each group will have two hard working students, two or three who might give a modicum of effort and two or three who will produce absolutely nothing and the entire group gets a group grade and there are no individual grades. This method allows every child to pass when only twenty percent of the students probably learned anything, and they are the students whose parents provide efforts to teach some of the old-school concepts and ways of solving math problems. The new teaching methods also include political opinions injected as part of the lessons even in the sciences. They use word problems which present a single political slant. Socialism is the base system for the best forms of governments. Everything is presented with a leftist slant and this programming indoctrination of the children, particularly the major colleges which are steeped in the alt-left.
Back to Israel as one of the favorite targets of the alt-left just as it has historically been a target of the alt-right. The left itself is tepid towards Israel at best and the far left is completely sold on the Palestinian propaganda because Israel won their last few wars and thus became the mean superpower in the Middle East. The fact is that the Arab World is thousands of times the size of Israel (check the map below). This map shows the Arab World including the twenty-one of twenty-two Arab States with Comoros off the map to the South while Israel is in Blue and has Iran and Turkey outlined in Red who are aligned with the Arabs against Israel. The main reason that Israel is able to survive is that currently the Arab world is torn into numerous camps and is unable to unite. The main focal points of the splits are Iran, Turkey, Saudi Arabia, Egypt and the several terrorist groups especially Hezballah who even has a base in South Americas in the Tri-Border Region. Currently, Iran aligned against Saudi Arabia is one of the main rift lines in the Middle East which has resulted in some interesting possibilities one of which has been the Arab World moving away from the Palestinians finally viewing them as a lost cause and hopelessly incompetent politically as well as being basically a dysfunctional society with no future even were they to replace Israel as they have become too violent and completely tainted and even loathsome. Even Qatar is attempting to distance themselves from the Palestinians who made a tactical error distancing themselves from President Trump, but their dissing President Trump enamored them with the Leftists who find President Trump to be an impostor or impostor who they refuse to accept as their President.

Arab World Showing Twenty-One of Twenty-Two States
with Comoros Off the Map South, Israel in Blue
and with Iran and Turkey outlined in Red
President Trump supports Israel which makes the leftists believe that their position of opposition to Israel as the correct position. Israel has taken the same types of lands in an even smaller piece without oil reserves and has taken their nation, the size (almost) of New Jersey, from a agricultural nation of Kibbutzim, small socialist communities, into a Capitalist engine which is amongst the leaders in technical innovations, medical discoveries, physics research, pharmaceutical inventions and remained one of the leaders in agricultural discoveries such as drip irrigation and many other accomplishments which are helping feed Africa. The fact that Israel has gone from a socialist society towards a more free-enterprise capitalist economy means that they are heading in what the leftists, especially the far left, believe is the wrong direction. It is also the same direction that President Trump is trying to aim the United States which is another reason he just has to be cast as evil. Israel and President Trump work to make their worlds a better place by providing a growing economy where most of the people can find work, if they desire to work, and not having the government support a large sector of the society. The left believes that many people who contribute in a different means to society, like street musicians and dancers, deserve to be supported by the government since what they choose to do does not provide sufficient income. President Trump would rather provide for these people to find work and perform their street acts as their hobby, not as their main contribution. Israel is also moving in that direction.
The left hates Israel largely because they are mean and use their military power to protect themselves. This is a large negative because they see the Palestinians as the underprivileged and people of color, despite they are not actually any different than the rest of the Arab people and the vast majority of the Palestinian Arabs are one or two generations away from their original nation of Egypt, Jordan, Syria, Iraq and beyond. The Arab nations consist of the entirety of the Middle East and North Africa and have an area and population thousands of times greater than Israel but Israel is considered the bully by the leftists. Why, because the Arab World has invested gazillions of dollars in propaganda and run support in the major colleges and universities casting this as a struggle where Israel used their military might to conquer Palestine in 1948 and further in 1967 wars. Both wars were started by the Arabs with the intent of destroying Israel and murdering every single Jew they would find after they won. Both wars had between five and seven nations against Israel and it was after a third loss in 1973 that the change came and all of a sudden it was no longer a half dozen Arab nations fighting Israel but Israel oppressing the Palestinian Arabs. The problem is there has never been a nation named Palestine so Israel did not conquer it. The Arabs mostly left their homes because their religious leader asked them to leave their homes, as they would be able to take the riches of the Jews once the Arab armies destroyed the cowardly Jews back in 1948 when the Arabs attacked Israel on the first day of its existence. Israel had been promised by the League of Nations after World War I to have the lands between the Jordan River and the Mediterranean Sea, all of it, plain and simple. Israel was not a result of the Holocaust as it predates that obscenity of mechanized slaughter and genocide of a people by almost twenty years. The United Nations is also presumably bound to support those borders but since it has become the United Totalitarians Club, thus they too hate Israel. The difficult part is that there are a majority of American Jews who will support the leftist President who will take America and support those who desire to destroy Israel. The other problem they will find out about far too late is that this leader will also be the one who will decide that the United States needs to be rid of those particular people who share this trait, this problem, they are Jewish. These leftists will at some point decide that the Jews are a problem which requires a solution, a final solution. The rising anti-Semitism has been plain to witness if one bothered to watch for it, and it has been growing on the left, the place the Jews said it could never arise. They were wrong and those who hate Israel will eventually turn on their own Jews. And as far as the United States turning against Israel, unfortunately that will come sooner than anybody in either country realizes.
Beyond the Cusp