The top senators with oversight of the Homeland Security Department are asking President Trump to swiftly take action on the growing number of vacancies among the agency’s top ranks, saying the unprecedented number of unfilled positions is preventing it from fulfilling its mission.

Seven of the 18 posts requiring Senate confirmation are currently vacant without a nominee pending, including three top positions. While Trump has repeatedly expressed his preference for leaders who serve in an acting capacity because it gives him more flexibility, Senate Homeland Security and Governmental Affairs Committee Chairman Sen. Ron Johnson, R-Wis., and ranking member Sen. Gary Peters, D-Mich., said that strategy was hurting the department.

“This widespread use of temporary leadership—individuals who, though perhaps qualified, do not serve with the imprimatur of having been confirmed by the Senate—makes it more difficult for the department to achieve its long-term strategic objectives,” the lawmakers wrote in a letter to Trump. They added government watchdogs, experts and former DHS officials have all “warned of the dangers of pervasive vacancies to government accountability and national security.”

Current acting DHS Secretary Kevin McAleenan announced in October he would step down at the end of the month. Trump did not name a replacement until Nov. 1, saying Chad Wolf, chief of staff to former Secretary Kirstjen Nielsen, had taken over as the temporary agency head. DHS and the White House later qualified that Wolf would not take over the position until the Senate first confirms him to serve as undersecretary for strategy, policy and plans. Senate Majority Leader Mitch McConnell, R-Ky., has said the chamber will act on Wolf’s undersecretary nomination next week.

Earlier this year, Trump dismissed several top leaders at DHS in quick succession. In addition to the secretary and Wolf’s Senate-confirmed role, the positions of deputy secretary, undersecretary for science and technology, undersecretary for management, chief of staff, general counsel, chief financial officer, U.S. Citizenship and Immigration Services director, Customs and Border Protection commissioner, Federal Emergency Management Agency administrator and others lack permanent leadership. Former DHS leaders and other observers have criticized Trump for the turmoil and many stakeholders have questioned the legality of his sidestepping of federal vacancies law.

Johnson and Peters called on Trump to “promptly” name nominees for Senate consideration.

“The Department of Homeland Security needs qualified, principled leaders to successfully carry out its many vital national security functions,” the senators wrote. “The American people deserve leaders who will ensure stability and accountability for the department.”