Natan Sharansky proposes a good litmus test for distinguishing between legitimate criticism of Israel and what crosses the line into anti-Semitism. He has three standards - demonization, double standards, and deligitimation. I think that the third standard should be discarded - the first two are sufficient to establish disproportionate focus, and thus by definition bias, and thus by definition anti-Jewish bias. And after all, one can be anti-Semitic and still advocate a Jewish state - by some accounts, both Stalin and Hitler dud at various points.