[DoodleDawg]

He will appear and he will testify or take the 5th.

I'm betting he won't. If the Senate subpoenas him the he will challenge it in court. The legal proceedings will last longer than the Senate trial will.

[Mariner]

The courts have no role in adjudicating a Senate subpoena.

Unless the Senate grants it to them through default.

But the Executive can enforce it once issued.

Because the House has ceded their constitutional authority to the courts does not mean the Senate must.