If the president's role is chief executive, vice president presides over the Senate, Electoral College elects president and vice president, what is the president pro tempore's role?

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President pro tempore of the United States Senate - Wikipedia, the free encyclopedia

The President pro tempore (IPA: /ˈproʊ ˈtɛmpəˌri/; also referred to as President pro tem) is the second-highest-ranking official of the United States Senate and the highest-ranking senator. The U.S. Constitution states the Vice President of the United States serves ex officio as President of the Senate, and is the highest-ranking official of the Senate even though he or she only votes in the case of a tie. During the Vice President's absence, the President pro tempore is the highest-ranking official in the Senate and may preside over its sessions. The President pro tempore is elected by the Senate; by custom, the President pro tempore is the most senior senator in the majority party. Normally, neither the Vice President of the United States nor the President pro tempore presides; instead, the duty is generally delegated to junior senators to help them learn parliamentary procedure.[1] The President pro tempore is third in the line of succession to the Presidency, after the Vice President of the United States and the Speaker of the House of Representatives.