A side note to my prior posts on the unitary executive. The Senate is our only institution that has a different ceremonial and functional head. The Majority Leader runs the Senate. But the President Pro Tempore is the leader who is mentioned multiple times in the Constitution. (The Majority leader is not mentioned). The President Pro Tempore is now just the most senior Senator in the majority, though that isn’t always how the post worked.
What does the President Pro Tempore do? Receive special communications (say, under the Twenty-Fifth Amendment). Preside over the Senate for some ceremonies when the VP cannot or will not. And so on.
Now why not have the Majority Leader do this? The Senate could, of course, make the President Pro Tempore the Majority Leader. Presumably they think that there is some value in separating these roles in a way that the House and the Executive do not. (The House could, of course, follow the British tradition and make the Speaker someone who is not in the party leadership, but we’ve never really done that.)
What about the Chief Justice and the Supreme Court? That’s another post.