Mayor Adams is attacking Assemblyman Zohran Mamdani, the Democratic nominee for mayor of New York City, over possible antisemitism and once identifying as “Black or African American” on his Columbia University application.

“It’s not excusable,” Mr. Adams said Monday during a CNBC interview.

Mr. Mamdani was born in Uganda and blamed a lack of choices on the 2009 application for choosing that label, along with also identifying as Asian. The school used race as a factor in determining admissions at that time. Mr. Mamdani ended up not being accepted.

Mr. Mamdani, a democratic socialist, told the New York Times he identifies as “an American who was born in Africa,” a description some online critics say could allow Elon Musk to also call himself African American.

“Most college applications don’t have a box for Indian-Ugandans, so I checked multiple boxes trying to capture the fullness of my background,” Mr. Mamdani told the paper.

That excuse was not good enough for Mr. Adams. “It was the wrong thing to do. So instead of saying, ‘I didn’t have enough boxes,’ how about saying, ‘I’m sorry,'” Mr. Adams said.

The mayor also said during Monday’s interview that Mr. Mamdani should apologize for reportedly sharing a video on social media that the Jewish advocacy group Stop Antisemitism said mocks Chanukah.

Mr. Mamdani has been criticized for his views on Israel and his refusal to condemn the phrase “globalize the intifada.”

When asked if he thought Mr. Mamdani was an antisemite, Mr. Adams said, “If he’s not he is truly misguided. You don’t mock Chanukah. You don’t mock it, you respect all faiths.”

“I think that there are actions we’re are seeing that, if he’s not antisemitic, then clearly there are things he needs to re-examine what he’s doing,” Mr. Adams went on to say.

Mr. Adams ditched the Democratic Party in favor of running for re-election as an independent candidate in this year’s election. Mr. Mamdani surged at the end of the primary season to upset a former New York governor, Andrew Cuomo, who had been leading in polls leading up to last month’s vote.

Mr. Cuomo is still weighing continuing his fight in the fall election by running on a third-party line. That could split the opposition vote against Mr. Mamdani between him, Mr. Adams, and the Republican nominee, Curtis Sliwa.