President Trump’s nominee to oversee the Environmental Protection Agency’s chemical safety division on Wednesday withdrew his name from consideration for the post in the face of mounting opposition.

The nominee, Michael L. Dourson, a longtime researcher whose studies often bolstered safety claims by manufacturers of pesticides, flame retardants and other products under federal scrutiny as possible public health hazards, had been working as an adviser to the agency while awaiting confirmation.

But the Senate never scheduled a confirmation vote for Mr. Dourson, who resigned from his job at the University of Cincinnati in October. And in recent weeks, two Republican senators came forward to say they would not support him.

Senator Thomas R. Carper, Democrat of Delaware and a member of the Environment and Public Works Committee, had pushed his colleagues to reject Mr. Dourson. He said Wednesday that his objections were not partisan.