I doubt there has been an increase in anti-Semitism as much as there has been an increase in the permissibility of the expressions of anti-Semitism and its amplification by the tools of social media.
A bit of history: American anti-Semitism was at its height in the 1930s during the crucial years just before World War II and the Holocaust. Those with anti-Semitic views did not disappear or alter their views in the immediate postwar years. What changed was that they did not feel comfortable expressing anti-Semitism without feeling some social stigma and rebuke both in public and even in social situations. Therefore, many in my generation grew up without hearing many anti-Semitic comments. That changed in the late 1960s with the tensions between Blacks and Jews; it changed again later with some hostility toward Israel and American Jews during the oil crisis of 1973 and 1979. And it has changed more rapidly since the turn of the century with the distance that has developed with the Holocaust. The tools of social networks and the internet magnify anti-Semitism and reinforce those who spew hatred.
No one can deny that the expressions of hatred have intensified the more polarized our society has become, and the explosion of anti-Semitism must be seen as but one dramatic, though not necessarily central, expansion of the expression of all hatreds — toward Muslims, toward immigrants, toward African-Americans, toward gays, toward the poor, toward any minority group, including white Americans without a college education who were at the core of President Donald Trump’s support in the November election.
Michael Berenbaum, “The Paradox of Today’s Anti-Semitism”, Jewish Journal (10-16 March 2017), 12.