The past several weeks have seen an outbreak of anti-Semitic threats and violence across the United States, stoking fear among Jews in small towns and major cities. During the two weeks of clashes in Israel and Gaza this month, the Anti-Defamation League collected 222 reports of anti-Semitic harassment, vandalism and violence in the United States, compared with 127 over the previous two weeks. Incidents are “literally happening from coast to coast, and spreading like wildfire,” said Jonathan Greenblatt, the A.D.L.’s chief executive. “The sheer audacity of these attacks feels very different.”... Many of the most recent incidents, by contrast, have come from perpetrators expressing support for the Palestinian cause and criticism of Israel’s right-wing government. “This is why Jews feel so terrified in this moment,” Mr. Greenblatt said, observing that there are currents of anti-Semitism flowing from both the left and the right. “For four years it seemed to be stimulated from the political right, with devastating consequences.” But at the scenes of the most recent attacks, he noted, “no one is wearing MAGA hats.”