MSNBC, where Mr. Halperin was an analyst on the influential show “Morning Joe,” said he would no longer serve as a contributor. HBO dropped a planned television adaptation of Mr. Halperin’s upcoming book about the 2016 presidential election. And by Thursday evening, his publisher, Penguin Press, said in a statement that it had canceled plans for the book entirely, “in light of the recent news.”

In a statement, Mr. Halperin denied any nonconsensual contact with the women who spoke to CNN, but he apologized for his behavior with his ABC News colleagues.

“During this period, I did pursue relationships with women that I worked with, including some junior to me,” Mr. Halperin said through a spokesman. “I now understand from these accounts that my behavior was inappropriate and caused others pain. For that, I am deeply sorry and I apologize. Under the circumstances, I’m going to take a step back from my day-to-day work while I properly deal with this situation.”

Mr. Halperin left ABC News 10 years ago, and a network spokesman said on Thursday that no complaints had been filed about him during his tenure.

The speed with which Mr. Halperin lost major television and book projects — his account of the 2016 election was among the most anticipated publishing releases of next year — reflected a growing national discussion about the misbehavior of powerful men. Mr. Halperin’s role as a chronicler of the race between Hillary Clinton and Donald J. Trump also put him at the center of an election that was defined by intense debates over gender, power, and the consequences of sexual harassment.