Sandy R. sent us this 2006 editorial by Grant Lilly, originally published by
AmericanDiplomacy.org.
It's a little longer than middling, but provides a fairly concise recent history of American views on political assassination.
Click anywhere on the excerpt to link up to the piece.

For thirty years, a presidential directive has barred American military leaders and intelligence officials from targeting particular individuals for elimination. The executive order that banned the practice of assassination, “targeted killing,” may have tamed the Central Intelligence Agency (CIA), dubbed a "rouge elephant" by Senator Frank Church (D-Idaho), but it also impeded the agency's and the military's ability to protect the United States.
Executive Order 11905, issued in 1976 by President Gerald Ford, reads: "No employee of the United States Government shall engage in, or conspire to engage in, political assassination." This mandate grew out of the 1975 session of the Select Committee to Study Governmental Operations, tasked by the Senate to review records of CIA involvement in assassination attempts on Fidel Castro of Cuba, Salvador Allende of Chile, and others. This body, also known as the Church Committee, after its chairman, described assassination as “unacceptable in our society” and called for an end to the practice.