On Monday, 11 bomb scares were called into Jewish community centers around the country. They were the latest in a string of such threats since the start of the year.

“Since the beginning of this year, we’ve seen four waves of these threats — we’ve never seen that before,” said David Posner, the director of strategic performance at the JCC Association of North America. Just one community center reported such a threat in all of 2016, he said.

The centers threatened on Monday were in Albuquerque; Birmingham, Ala.; Buffalo; Chicago; Cleveland; Houston; Milwaukee; Nashville; St. Paul; Tampa, Fla.; and Tulsa, Okla. Like the earlier threats, they were deemed hoaxes, but not before several of the centers were evacuated as a precaution.

Mr. Trump has been criticized as slow to condemn anti-Semitic comments, and his candidacy was hailed by white nationalists and white supremacists throughout 2016.