President pro tempore of the United States Senate
Officially the vice president is the person in charge of the Senate, but they are not a Senator.  Patty Murray (D-WA) is the president pro tempore, the first woman to hold this position. When the vice president cannot be in charge, the president pro tempore is in charge of the Senate. Many people still think of the president pro tempore as de facto president of the Senate. Benjamin Wade was only one vote away from becoming the president of the United States due to the impeachment of Andrew Johnson. No president pro tempore has taken over the presidency as of March 2020.