In 1867, Andrew Johnson fired his Secretary of War, in defiance of the Tenure of Office Act, which barred a President from removing Cabinet Officials without Senatorial approval. The House impeached him, and the Senate came one vote shy of removing him from office.

In 2012, Barack Obama waives a federal statute without being granted the authority to do so. The Health Care Act grants the President that authority; the No Child Left Behind Bill does not.

The Supreme Court later declared the Tenure of Office Act unconstitutional. The  court so treating the Health Care Act is the only thing which might make violating it a non-impeachable offense.

In the meantime, proggies, enjoy your tyrant Constitutional Scholar.