Denying the administration permission to proceed with arms sales and program changes, or denying Senate leadership permission to proceed with nominations and non-controversial legislation is a high-risk, but often useful, tool for extracting promises of policy change.
By law, certain arms transfers and foreign aid programs must be notified to Congress 15 to 30 days in advance. By custom, the Chairs and Ranking Members of the committees of jurisdiction are permitted to place an informal "hold" on these actions, either for informational purposes (a temporary hold until additional information is provided) or for substantive reasons (a permanent hold until conditions are met). There is no clear, legal procedure for resolving these holds, and at times an administration has proceeded over congressional objections.
In the Senate, which operates largely by unanimous consent, the objection of a single Sen.can prevent action on legislation or nominations unless or until the Majority Leader decides to make a motion to proceed and has the time and votes to limit debate.
Be judicious about using holds, since they may cause unintended or perverse outcomes (such as shutting down production lines, losing short-window opportunities, or dislocating nominees' families).
Holds are most effective for requiring the administration to uphold existing policies more rigorously or coherently, rather than to force a change in policy.
Clearly explain the reasons for your hold and the outcomes you are seeking. This will increase public pressure and sympathy for the desired policy changes.
No Guns for the Philippines. After his inauguration in June 2016, Philippine President Rodrigo Duterte launched a "war on drugs" that resulted in thousands of extrajudicial killings by the police and affiliated hit squads. When the State Department began considering the sale of 26,000 assault rifles to the Philippines' national police later that summer, Sen. Ben Cardin indicated his intention to place a hold on the proposal. His intervention strengthened opponents of the sale within the State Department, and the sale was shelved.
Blocking Surplus Helicopters to Mexico. In April 1996, Sen. Jesse Helms blocked the transfer of 20 excess UH-1H Huey helicopters to Mexico, arguing that they would be used for counterinsurgency purposes rather than the counternarcotics mission for which they were intended. In exchange for lifting his hold, Helms obtained assurances that they would be subject to U.S. end-use monitoring, and he followed up with questions on how they were being used. However, a subsequent GAO report concluded the helicopters were of "limited usefulness" for some counternarcotics missions and found no evidence that the helicopters were being used to support the 12 special Mexican Army units involved in drug-interdiction activities.
Preventing the Sale of Attack Aircraft to Nigeria. By the time the proposed sale of 12 Super Tucano attack aircraft to Nigeria was publicly reported in May 2016, Senate staff had already expressed strong opposition. There had been no accountability for the December 2015 Zaria massacre, in which hundreds of Shia Muslims were killed by the Nigerian Army. Staffers asked for briefings and assurances that the aircraft would not be used for bombing civilian targets, and they demanded that the U.S. obtain human rights commitments from the Nigerian military. President Trump ultimately greenlighted the sale in April, 2017.