Top Democrats in Congress want the FBI to determine whether the facilities and equipment President Trump uses to access classified information while at his Florida resort are vulnerable to foreign exploitation, after reports that a Chinese national managed to clear security at the Mar-a-Lago Club with a thumb drive containing malicious software.

In a Wednesday letter to FBI Director Christopher A. Wray, Senate Minority Leader Charles E. Schumer (N.Y.), Judiciary committee ranking member Sen. Dianne Feinstein (Calif.) and Intelligence committee vice chairman Sen. Mark R. Warner (Va.) stressed that the “incident raises very serious questions regarding security vulnerabilities at Mar-a-Lago, which foreign intelligence services have reportedly targeted.”

“As the White House Communications Agency and Secret Service coordinate to establish several secure areas at Mar-a-Lago for handling classified information when the President travels there, these potential vulnerabilities have serious national security implications,” they wrote.

They also asked Wray what additional steps would be “needed to detect and deter adversary governments or their agents” from conducting electronic surveillance or gaining access to materials at Mar-a-Lago and Trump’s other properties.

The Secret Service will brief the leaders of the House Oversight Committee on Thursday morning about the Mar-a-Lago security breach, said Chairman Elijah E. Cummings (D-Md.). Agency leaders will sit with Cummings and ranking member Rep. Jim Jordan (R-Ohio) to go over what happened and how they plan to prevent a relapse.

Cummings said he is “concerned when people are able to get into the facility in Mar-a-Lago and [are] roaming around with all kinds of communications equipment.”

“I will do everything in my power to make sure the president is properly protected. . . . I want to make sure that the Secret Service is being the very best that they can be, and I think we want to find out exactly what kind of security they have down there in Florida,” he said.

According to court documents, Yujing Zhang went to Mar-a-Lago on Saturday, at first claiming to be there to use the swimming pool, but later stating she was there for a meeting of the United Nations Chinese American Association — an event that did not exist. Due to language barriers and confusion on the part of security officials, who thought she was the relative of a club member, Zhang was able to enter the resort and get past security barriers into an area near Trump’s private residence.

Upon questioning, Zhang referred to a person named “Charles” as the contact who had invited her to the club. It is unclear if that was a reference to Charles Lee, an event promoter who sometimes sold tickets to Mar-a-Lago events. But Lee occasionally acquired tickets to banquet events from Li “Cindy” Yang, the founder of a south Florida massage parlor linked to a sex trafficking and prostitution ring, whose visits to Mar-a-Lago caught the attention of congressional Democrats last month. Yang sold that business years before authorities in Florida targeted its current owners.

In a March 15 letter to Wray, the top Democrats on the House and Senate Judiciary and Intelligence Committees asked the FBI to investigate whether Yang had used her connections to Trump and his club to facilitate business opportunities for Chinese executives. Her activities “could permit adversary governments or their agents access to these same politicians to acquire potential material for blackmail or other even more nefarious purposes,” they wrote to Wray, Director of National Intelligence Daniel Coats and Secret Service Director Randolph Alles.

In their Wednesday letter regarding Zhang, Senate Democrats reminded Wray they had not yet received a response to their previous request.

Separately, House Intelligence Committee chairman Rep. Adam B. Schiff (D-Calif.) on Wednesday asked Wray, Coats and Alles for a briefing about Zhang, whether authorities could connect her presence at Mar-a-Lago to Yang and how China could be trying to target Trump’s properties or businesses for leverage with the president.