George W. Bush finally found a decent Secretary of Defense in Robert Gates. The Obama Administration continued Bob Gates through Obama's first term. Obama had no military experience other than as a Social Worker in south side Chicago. Continuing Bob Gates assured the World (including NATO) that at least of of the NCAs was competent.
The Trump Administration can accomplish all of this with Ash Carter and get somebody smart that understands "the Iran Deal."
Senator Jeff Sessions has been mentioned as a candidate for AG and SECDEF. The Republicans do not have too many senators in the Senate. Consideration will be given to which party will gain by a Senator being elevated to the Cabinet.
I am not a fan of Big Government Newt Gingrich. He's smart and should be utilized by Trump as appropriate. Secretary of State might be a good fit. I do not believe SECDEF would be.
The following is extracted from Wikipedia:
"Carter was nominated by President Obama to be the 25th United States Secretary of Defense on December 5, 2014.
"In his nomination hearing before the Senate Armed Services Committee, he said he was “very much inclined” to increase U.S. military aid to Ukraine Speaking on the Middle East, he said the U.S. must militarily ensure a “lasting defeat” of Islamic State (ISIL) forces in Iraq and Syria. He said he is not in favor of increasing the rate of prisoner releases from Guantanamo Bay. He also opined that the threats posed by Iran were as serious as those posed by the ISIL forces.
"He was approved unanimously on February 1, 2015, by the Senate Armed Services Committee. He was confirmed by the Senate on February 12 by a vote of 93–5 and sworn in by Vice President Joe Biden on February 17.
"The United States is coordinating closely with Saudi Arabia, Sudan, Egypt, Qatar, and the other Sunni Arab allies in the Saudi Arabian-led intervention in Yemen against the Shia Houthis and forces loyal to former President Ali Abdullah Saleh, who was deposed in the 2011 uprising.
"In May 2015, Carter warned China to halt its rapid island-building in the South China Sea.
In October 2015, Carter has condemned Russian air strikes against ISIL and other rebel groups in Syria.
"On October 8, 2015, Carter, speaking at a meeting of NATO defence ministers in Brussels, said he believed Russia would soon start paying the price for its military intervention in Syria in the form of reprisal attacks and casualties.
"A controversy arose in December 2015 when it was revealed that Carter had used personal email account when conducting official business as Secretary of Defense.
"In January 2016, at Carter's direction, the Department of Defense opened all military roles to women, overriding a request by the Marine Corps to continue to exempt women from certain positions. In June 2016, Carter announced that transgender individuals would be allowed to join and openly serve in the military."
A Trump Administration would gain worldwide credibility by selecting Ashton B. Carter as its first SECDEF. I would expect a Trump Administration to continually select the best person available. General Flynn might be qualified in a second Trump Administration.