A leading Senate Republican wants to know if any White House staffers were involved in the prostitution scandal that struck the Secret Service this month.

Sen. Charles GrassleyCharles (Chuck) Ernest GrassleyGOP chairman in talks with 'big pharma' on moving drug pricing bill Senate GOP urges Trump administration to work closely with Congress on NAFTA This week: House GOP regroups after farm bill failure MORE, the ranking member of the Senate Judiciary Committee, penned a letter to agency leaders late Friday asking whether any civilians working for the administration had accompanied the Secret Service and military personnel to Colombia to prepare security for President Obama's recent visit.

The Iowa Republican said it's his "understanding" that the Secret Service advance team "ordinarily … works closely" with both the White House Communications Agency (WHCA) and the White House Office of Advance.

"It is also my understanding … that the Secret Service may help reserve rooms for representatives for these offices," Grassley wrote to Secret Service Director Mark Sullivan and Charles Edwards, acting inspector general for the Department of Homeland Security. 

With that in mind, Grassley is wondering if the current investigations are limited to the Secret Service agents and military personnel involved in the incident, or if the probe includes any White House staffers who might have been in Cartagena that night.

"Did the Secret Service reserve rooms … for representatives of the WHCA or the White House advance team?" Grassley asks. "If so, have records for overnight guests for those entities been pulled as part of the investigation … ?"

Eleven Secret Service agents have been implicated in the headline-grabbing scandal, which also involved members of the military, assigned to set up security for Obama's trip. The Americans allegedly caroused with prostitutes before bringing as many as 21 women back to their hotel. The incident has raised questions about whether the president's security was ever compromised. 

The Secret Service launched an immediate investigation, and this week the agency announced that six of the 11 agents involved will soon leave the agency. The others have been suspended pending further investigation.

Grassley also wants to know whether there were other agents at other hotels who might have been involved. 

"If so, were records from those other hotels pulled?" he asked.

The Iowa Republican has asked the officials to respond "as soon as possible."