Bill > SRes4

This resolution notifies the President of the United States about the election of Senator Charles E. Grassley as President pro tempore of the Senate. A President pro tempore (often abbreviated as "President pro tem") is a senior member of the Senate who presides over the Senate in the absence of the Vice President and is traditionally the most senior member of the majority party. In this case, Senator Grassley, a Republican from Iowa, has been elected to this important leadership role, which places him second in the line of succession to the presidency after the Vice President. The resolution serves as a formal communication to the President, informing him of this significant change in Senate leadership, which is a customary practice following the election of a new President pro tempore.

https://www.congress.gov/bill/119th-congress/senate-resolution/4/all-info