How can contesting congressional subpoenas be an impeachable offense if the president has sufficient legal grounds in so doing that the Supreme Court agrees to review the controversy? From Alan Dershowitz at thehill.com:
The decision by the Supreme Court to review the lower court rulings involving congressional and prosecution subpoenas directed toward President Trump undercuts the second article of impeachment that passed the House Judiciary Committee along party lines last week.
That second article of impeachment charges President Trump with obstruction of Congress for refusing to comply with the congressional subpoenas in the absence of a final court order. In so charging him, the House Judiciary Committee has arrogated to itself the power to decide the validity of subpoenas, and the power to determine whether claims of executive privilege must be recognized, both authorities that properly belong with the judicial branch of our government, not the legislative branch. The House of Representatives will do likewise, when it votes to approve the articles, as the chamber is expected to do so Wednesday.