Actually, this view deserved it's own thread to be seen and properly debated. As to the debate part, tell me why I am incorrect.
No it didn't. It's an unfounded notion that could have been posted as part of existing discussions, if you were wondering about it. It doesn't merit a thread with a lot of debate.
"As to the debate part, tell me why I am incorrect."
To be unconstitutional there would have to be some provision in the constitution that means they can't do it. There isn't. In fact it says the Senate has the "sole power to try impeachments", as you know. The Senate has the right to do that how they like.
You're using a comparison to judicial process to argue they can't, but that's not a constitutional argument. And it's wrong in any case. The criminal courts routinely have witnesses, including witnesses that didn't come up during an initial investigation. There's absolutely no rule of law saying there can't be a new witness in a criminal trial.
The correct comparison to use would be comparing impeachment by the House to a grand jury indictment, not to discovery. Discovery is part of the trial process. And if the Senate wanted to engage in discovery, they are empowered to do so.