This week brought the first public hearings in the impeachment inquiry into Donald Trump’s dealings with Ukraine. Next week, they will continue with many more witnesses set to testify.

The hearings have been long – at times riveting, at times tedious — with partisan bickering on full display.

They are also historic. It’s a rare thing for Congress to use this tool crafted by the framers to hold the president’s power in check. My guest, Harvard law professor Cass Sunstein, says that’s a good thing.

Sunstein is the author of “Impeachment: A Citizen’s Guide.”

Diane spoke with Sunstein Friday morning as Marie Yovanovitch testified in Congress. She asked what our founding documents say should – and should not – be considered an impeachable offense.