Here is my take on why Obama will not be impeached (at least in this term) for the unconstitutional assassination of an American citizen in a country where no war has been declared.
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort.
— U.S. Constitution - Article 3 Section 3
Unfortunately, under the Patriot Act we can't impeach President Obama for his assasination of Anwar al-Awlaki. We should have pushed to impeach President Obama when he went to war with Libya without getting Congresses approval and making a declaration. This went against the Constitution that he swore to defend when he was innagurated as President.