Who is qualified to be the Commander in Chief?

Wesley Kanne Clark, Sr graduated at the head of his class in West Point in 1966.  He retired as a 4 star general (O-10) from the Army May 2, 2000.  By most reasonable criteria, he was qualified to be CINC.

Colin Luther Powell (born April 5, 1937) is an American statesman and a retired four-star general (O-10) in the United States Army. He was the 65th United States Secretary of State, serving from 2001 to 2005, the first African American to serve in that position.  During his military career, Powell also served as National Security Advisor (1987–1989), as Commander of the United States Army Forces Command (1989) and as Chairman of the Joint Chiefs of Staff (1989–1993), holding the latter position during the Persian Gulf War.  By most criteria, Colin Powell would be qualified to be a CINC.

John Sidney McCain III (born August 29, 1936) is the senior senator from Arizona.  He was the Republican presidential nominee in 2008.  McCain followed his father and grandfather, both four-star admirals, into the United States Navy, graduating from the U.S. Naval Academy in 1958.   He became a naval aviator, flying ground-attack aircraft from aircraft carriers. In October 1967, while on a bombing mission over Hanoi, he was shot down, seriously injured, and captured by the North Vietnamese.  He was a prisoner of war until 1973. McCain experienced episodes of  torture, and refused an out-of-sequence early repatriation offer. His war wounds left him with lifelong physical limitations.

He retired from the Navy as a captain (O-6) in 1981 and moved to Arizona, where he entered politics. Elected to the House in 1982, he served two terms, and was then elected to the Senate in 1986, winning re-election easily four times, most recently in 2010. While generally adhering to conservative principles, McCain at times has had a media reputation as a "maverick" for his willingness to disagree with his party on certain issues.

Wesley Clarke (and later Donald Trump) did not see how experience as a POW was of great benefit for being the CINC.

Marco Antonio Rubio (born May 28, 1971) is an American attorney and politician and junior United States Senator from Florida.  Rubio previously served as Speaker of the Florida House of Representatives.  He is a candidate for the Republican nomination for President of the United States, in the 2016 presidential election.

Rubio is a Cuban American from Miami. He is a graduate of the University of Florida and the University of Miami School of Law. In the late 1990s, he served as a City Commissioner for West Miami and was elected to the Florida House of Representatives in 2000, representing the 111th House district.

Later in 2000, Rubio was promoted to be one of two majority whips, and in 2002 was appointed House Majority Leader by Speaker Johnnie Byrd. He was elected Speaker of the Florida House, and served as Speaker for two years beginning in November 2006. Upon leaving the Florida legislature in 2008 due to term limits, Rubio started a new law firm, and also began teaching at Florida International University, where he continues as an adjunct professor.

Rubio ran for United States Senate in 2010, and won that election. In the U.S. Senate, he chairs the Commerce Subcommittee on Oceans, Atmosphere, Fisheries, and Coast Guard, as well as the Foreign Relations Subcommittee on Western Hemisphere, Transnational Crime, Civilian Security, Democracy, Human Rights and Global Women's Issues. He is one of three Latino Americans serving in the Senate. On April 13, 2015, Rubio announced that he would forgo seeking reelection to the Senate to run for President.

Barack Hussein Obama II ( born August 4, 1961) is an American politician serving as the 44th President of the United States, the first African American to hold the office. Born in Honolulu, Hawaii, Obama is a graduate of Columbia University and Harvard Law School, where he served as president of the Harvard Law Review. He was a community organizer in Chicago before earning his law degree. He worked as a civil rights attorney and taught constitutional law at University of Chicago Law School between 1992 and 2004. He served three terms representing the 13th District in the Illinois Senate from 1997 to 2004, and ran unsuccessfully in the Democratic primary for the United States House of Representatives in 2000 against incumbent Bobby Rush.

In 2004, Obama received national attention during his campaign to represent Illinois in the United States Senate with his victory in the March Democratic Party primary, his keynote address at the Democratic National Convention in July, and his election to the Senate in November. He began his presidential campaign in 2007 and, after a close primary campaign against Hillary Rodham Clinton in 2008, he won sufficient delegates in the Democratic Party primaries to receive the presidential nomination. He then defeated Republican nominee John McCain in the general election, and was inaugurated as president on January 20, 2009. Nine months after his inauguration, Obama was named the 2009 Nobel Peace Prize laureate.

Barack Obama had no military experience before taking office and has been a terrible CINC.  His current Secretary of Defense, Aston B. Carter is doing a good job.  Illustrating that appointees are important.

Carter served as US Assistant Secretary of Defense for International Security Policy during President Clinton's first term, from 1993 to 1996, responsible for policy regarding the former Soviet states, strategic affairs, and nuclear weapons policy. He was Under Secretary of Defense for Acquisition, Technology, and Logistics from April 2009 to October 2011, with responsibility for procurement of all technology, systems, services, and supplies, bases and infrastructure, energy, and environment, and more than $50 billion annually in R&D. He was then Deputy Secretary of Defense from October 2011 to December 2013, serving as the chief operating officer of the DOD overseeing more than $600 billion per year and 2.4 million civilian and military personnel, and managing global 24/7 operations. He was confirmed unanimously by the U.S. Senate for both the number-two and number-three Pentagon positions.

Carter's academic credentials are respectable.  Carter received a B.A. in his double-major of Physics and Medieval History from Yale University, summa cum laude, in 1976. He then became a Rhodes Scholar and studied at the University of Oxford, from which he received his doctorate in Theoretical Physics in 1979. He worked on quantum chromodynamics, the quantum field theory that was then postulated to explain the behavior of nuclear reactions and the structure of subatomic particles. He was a postdoctoral fellow research associate in Theoretical Physics at Rockefeller University from 1979 to 1980, and a research fellow at the MIT Center for International Studies from 1982 to 1984.

Carter taught at Harvard University, beginning in 1986. He ultimately rose to become chair of the International & Global Affairs faculty, and Ford Foundation Professor of Science & International Affairs, at the Belfer Center for Science and International Affairs at Harvard's John F. Kennedy School of Government. Carter is author or co-author of 11 books and more than 100 articles on physics, technology, national security, and management.

The United States Senate should ensure that either the President or the Secretary of Defense (National Command Authorities) is qualified to be CINC.  Barack Obama II nor Chuck Hagel were.