WASHINGTON — An executive order signed Wednesday that extends civil rights protection to Jews is likely to strengthen the hand of President Trump’s Education Department, where the department’s civil rights chief has been investigating some of the nation’s most elite universities for anti-Jewish bias.

Mr. Trump, at a Hanukkah celebration at the White House, opened the door on a case-by-case basis to essentially defining Judaism as a race or national origin, not just a religion, under the Civil Rights Act. His order also expanded the definition of anti-Semitism to include some anti-Israel sentiments. Both moves had been pushed by Kenneth L. Marcus, the head of the Education Department’s Office for Civil Rights, for years.

“This is our message to universities: if you want to accept the tremendous amount of federal dollars that you get every year, you must reject anti-Semitism, it’s very simple,” Mr. Trump said at the signing ceremony.

Even before the order, Mr. Marcus was already deeming Judaism a “national origin,” like Italian or Polish, to strengthen a campaign against what he sees as rampant anti-Semitism in higher education. At both the University of Pennsylvania and Stanford, Mr. Marcus has opened “national origin” investigations to determine whether qualified applicants were rejected because of their Judaism.