The conduct is still impeachable even if he can declassify, explicitly or impliedly. (And I agree he can disclose whatever he wants to whomever he wants. But I

The conduct is still impeachable even if he can declassify, explicitly or impliedly. (And I agree he can disclose whatever he wants to whomever he wants. But I also believe the Secretary of State has similar powers, albeit more narrowly circumscribed. Note that both Hillary Clinton and her predecessor, Colin Powell, used private e-mail servers.) The phrase "high crimes and misdemeanors" means the opposite of what people intuitively think. Elected officials entrusted with state powers are held (or were at the time of the founding deemed to be held) to higher ethical and moral standards than regular citizens. A "high crime" would be misbehavior by someone in a high office. See https://en.wikipedia.org/wiki/High_crimes_and_misdemeanors https://en.wikipedia.org/wiki/High_crimes_and_misdemeanors Wantonly reckless behavior wrt to national security is, I would hope, indisputably impeachable. But in any event what's impeachable is entirely up to Congress as a practical matter--their decision is unreviewable except by the ballot box.