Each senator has one vote. The vice president may vote only when the Senate is deadlocked by a tie. In the absence of the vice president the Senate is presided over by a president pro tempore, who, by the terms of an act passed by Congress in 1947, is next after the Speaker of the House of Representatives in the order of succession to the U.S. presidency. The president pro tempore participates in debates and has a vote. Those regarded as most important are the committees on Appropriations, Foreign Relations, and Rules and Administration.
Events sometimes focus public attention on the other standing committees.