He described the anonymous sources who he said gave him information on a bomb at the port as being in the Midwest and that they were fearful of reprisals from Andrew G. McCabe, the acting director of the F.B.I.

“These are American patriots who spent decades even before D.H.S. was formed in service to our country saving our country from terrorists’ attacks,” Mr. Webb said, referring to the Department of Homeland Security.

The Maersk Memphis, which was built in 2007 and sails under the American flag for Maersk Line, a United States corporation, arrived at the port on Wednesday evening, Signe Brink Wagner, a company spokeswoman, said in an email.

“When informed about the threat, the vessel was immediately evacuated and all crew brought safely ashore,” she wrote. “We expect the vessel will resume its voyage according to schedule.”

Erin P. Dhand, a spokeswoman for the operator of the port, South Carolina Ports Authority, said in a statement on Thursday that it was “operating as usual with minimal impacts to our operations from last night’s incident.”

The United States Coast Guard said on Twitter that the person who reported the threat was being questioned by the authorities. But it was not clear which agency had detained the person, who was not identified.