Senate Homeland Security Chairman Sen. Gary Peters, D-Mich., right, asks questions of U.S. Secret Service Acting Director Ronald Rowe and FBI Deputy Director Paul Abbate during a Joint Senate Committee on Homeland Security and Governmental Affairs and Senate Committee on the Judiciary hearing examining the security failures leading to the assassination attempt on Republican presidential candidate former President Donald Trump on July 30 in Washington. Associated Press

WASHINGTON — A U.S. Senate committee investigating the attempted assassination of former President Donald Trump in Butler County, plans to issue an interim report by the end of the month, the panel's chairman said Tuesday.

U.S. Sen. Gary Peters, D-Mich., said there were still plenty of questions to be answered and people to interview, but the report would reveal what the committee has uncovered so far. He said the report would be issued when the Senate recessed for the election. The Senate is supposed to leave Washington on Sept. 27.

“We are going to put out what we’ve learned so far, but we need more information,” Peters said at a breakfast sponsored by the Christian Science Monitor. “Part of what we found so far leads to further questions. It is those questions we need answers to, and those questions are going to require additional interviews, additional documents for us to get the answers to our questions.”

But some of that information has proven difficult to obtain, U.S. Sen. Richard Blumenthal, D-Conn., chair of the panel’s investigations subcommittee, told reporters at the Capitol later on Tuesday. Blumenthal said the U.S. Department of Homeland Security was “stonewalling” the investigation, which he called “immensely frustrating and outrageous.”

Blumenthal raised the possibility that the Senate would subpoena the information if the DHS was not forthcoming.

“We’ve received a communication that is an insult to our intelligence as well as our proper role as an oversight body,” Blumenthal said. “They’ve just completely failed to be forthcoming.”

DHS said in a statement that the agency, including the Secret Service, has given the Senate several briefings, around 2,500 pages of documents, and more than 50 hours of transcribed interviews, while also cooperating with the House task force, the White House's review, the agency's inspector general, and the Government Accountablity Office, the investigative arm of Congress.

“DHS remains committed to working in good faith and making every effort to cooperate with the appropriate and relevant investigations into July 13 to identify how this happened and how to prevent it from happening again,” the agency said. “Claims that the Department and Secret Service are not cooperating are false and fail to recognize the robust response and ongoing work to meet Congress’ oversight requests, and our clear commitment to accountability for the events of July 13.”

Peters said the committee also had questions about Sunday's apparent assassination attempt at Trump’s West Palm Beach, Fla., golf club. He said the panel would be briefed on the incident.

“Clearly, what happened in Florida is very troubling,” Peters said. “To have somebody that can be waiting for allegedly 12 hours and not be spotted by Secret Service and not understand why that individual was there, it certainly raises many questions, and we're going to want answers to that as well.”