…It is an interesting question, actually, and one that doesn’t lend itself to a simple answer.
The wiki article called “Who is a Jew?” is literally longer than one on Quantum mechanics 
Where I am from, it was considered first and foremost an ethnicity, and therefore an inalienable, inalterable, and inescapable part of one self, - so much so that it was recorded in one’s passport, just like any other ethnicity would, yet with bigger ramifications. And in fact today, overwhelming majority of American (Ashkenazi) Jews can indeed be unambiguously identified by a genetic test with a 100% sensitivity and specificity.
My intention with providing this tidbit is not to derail the thread and get myself into trouble with moderators, but to take an opportunity to illustrate yet another facet of the complexity of the Jewish condition in America and around the world (where many American Jews or their recent ancestors came from) that may be hard to fully appreciate from the outside - a facet that, along, of course, with other aspects of Jewish history, may in fact be very relevant to understanding how many Jews are perceiving what is now happening on college campuses.