I have to agree that passing unconstitutional laws are not criminal. Maybe they should be but they're not. It's up to the Supreme Court to strike down such laws.
The greatest impeachable offense, of course, is attacking Afghanistan and Iraq.
http://www.lcnp.org/global/iraqstatement3.htm
"The United Nations Charter is a treaty of the United States, and as such forms part of the "supreme law of the land" under the Constitution, Article VI, Clause 2. The UN Charter is the highest treaty in the world, superseding states’ conflicting obligations under any other international agreement. (Art. 103, UN Charter)
Under the UN Charter, there are only two circumstances in which the use of force is permissible: in collective or individual self-defense against an actual or imminent armed attack; and when the Security Council has directed or authorized use of force to maintain or restore international peace and security. Neither of those circumstances now exist. Absent one of them, U.S. use of force against Iraq is unlawful."