Who determines the powers of the Chief Justice in impeachment trials?

Question

There's a lot of talk about how unclear it is what John Roberts has the power to do in the impeachment trial.

I've seen claims that he can call witness and claims that he can't; there are articles about how it's unclear whether he can break ties, like the vice president. There are probably a lot more areas of confusion as to what he can do.

However, the Constitution only really matters when it is interpreted.

Who can formally decide what the Chief Justice can and can't do in an impeachment trial? The courts? The Senate? Where are his powers defined?

Answer 1

US federal impeachment trials are governed by the Rules of the Senate. The US Constitution has the Chief Justice preside over the Senate for an impeachment trial of the President and that's all it says. The confusion is whether he has all of the same powers as the President of the Senate (normally the US Vice-President). Generally, the thought is that he probably does, although this hasn't been tested (never came up in Clinton's trial and Andrew Johnson's trial had different rules).

In reality, it's highly unlikely the Chief Justice will "go rogue" against the wishes of the Senate Majority Leader. Presiding over the Senate is a mostly ceremonial role (even in regular business). And in the end, the Senate can always vote on whether to accept the Chief Justice's actions. It's not quite as impossible like Queen Elizabeth withholding Royal Assent on something, but that's the level we're talking about.