U.S. Secret Service Director Mark Sullivan. (Brendan Hoffman/Bloomberg)

U.S. Secret Service Director Mark Sullivan is slated to make his first public appearance Wednesday before lawmakers to discuss his agency’s response to a scandal that earned the storied institution embarrassing headlines around the world.

Sullivan will appear at a hearing held by the Senate Homeland Security and Governmental Affairs Committee alongside Homeland Security Acting Inspector General Charles K. Edwards, who is poised to tell lawmakers that the agency is cooperating with a separate probe into its response to a scandal that unfolded ahead of a trip last month by President Obama to Colombia.

Sen. Joseph I. Lieberman (I-Conn.), who chairs the homeland security panel, said Tuesday that lawmakers are especially eager to hear from Sullivan, adding that the hearing “will be an important day for the agency and for him.”

Pay special attention today to how remorseful Sullivan appears during his opening statement and answers to questions from senators. In the initial days of the scandal, lawmakers held the Secret Service in high esteem for its response, especially when compared to how the General Services Administration was dealing with the fallout from a spending scandal involving a high-priced employee conference held in Las Vegas.

Members of Congress faulted former GSA administrator Martha Johnson for quitting in the hours after the scandal instead of staying put to fix the problems — as Sullivan opted to do. But Johnson earned back a considerable amount of good will from some of her critics when she made a starkly emotional, apologetic opening statement at the start of a House hearing on the scandal.

Sullivan enjoys virtually rock-solid support among lawmakers on Capitol Hill. Sen. Susan Collins (R-Maine), ranking Republican on the Homeland Security committee, said recently that Sullivan and his agency enjoy strong congressional support because “we have seen Secret Service agents literally throw themselves in front of presidents. It’s impressive.”

But if Sullivan appears too defensive — or fails to assure lawmakers Wednesday that the night of partying, drinking and sex in Cartagena was an isolated incident — some lawmakers concede that their support for the director could wane.

At the White House Tuesday, Press Secretary Jay Carney wouldn’t say whether President Obama believes Sullivan should explicitly apologize publicly for the scandal, but said “He has great faith in the Secret Service. He believes the director has done an excellent job moving very quickly to have this matter investigated and took action as a result of that investigation.”

Sullivan is expected to provide a strong defense and tell lawmakers that “none of the individuals involved in misconduct had received any specific protective information, sensitive security documents, firearms, radios or other security-related equipment in their hotel rooms,” according to Sullivan’s prepared testimony, first obtained by The Post’s Joe Davidson.

Sen. John McCain (R-Ariz.), a ranking member on the committee, said Tuesday that he hopes the hearing will allow Congress “to begin to ask and try to determine, Did they miss any signs over the years prior to Cartagena that should have told them that this was going to be a problem?”

McCain and his colleagues should find comfort in Edwards’s comments. According to his testimony, “the Secret Service has been completely transparent and cooperative with our inspectors and investigators. We have high regard for the effort the Secret Service has put forth thus far.”

Edwards is slated to testify that his office was first briefed on the situation April 13, the day after Secret Service personnel implicated in the scandal were sent home from Cartagena. Sullivan and Edwards met in person twice, May 1 and May 4, and Edwards said Sullivan “has repeatedly stated to me his commitment to conduct a complete and thorough investigation. His actions so far have demonstrated that commitment.”

Edwards’s office plans to review the notes from interviews with nearly 200 Secret Service employees who were in Colombia and 25 employees at the hotels in Colombia. He also plans to review how many and what types of polygraph tests were conducted of agency personnel, according to his testimony.

“I want to stress that the Secret Service’s efforts to date in investigating its own employees should not be discounted,” Edwards plans to tell lawmakers. “It has done credible job of uncovering the facts and, where appropriate, it has taken swift and decisive action.”

Staff writers David Nakamura and Rosalind S. Helderman contributed to this report.

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