US Secretary of Defense James Mattis has done an excellent job ensuring congressional support for a much increased defence budget, strengthening alliances, building partnerships and being an inspirational leader for US defence forces. Nevertheless, rumours about his future abound. Secretary Mattis may well last the full first term of the Trump administration, but if he leaves after November's midterm elections, who is a logical replacement? And could Nikki Haley's resignation as US Ambassador to the United Nations overnight be a factor in all this?

Senior South Carolina Senator Lindsay Graham's recent performance during the Brett Kavanaugh hearings and his dramatic turn to be more "Trump than Trump" is driven by two things. First, that he has to get back in the good graces of the Republican Party following the death of his close friend and fellow maverick, John McCain. Without the protection of Senator McCain flying top-cover, Graham can’t be the independent he fancies himself being and still be in the good graces of the Republican leadership, like majority leader Senator Mitch McConnell.

Second, to escape the Senate and truly come into his own, Senator Graham – a retired Air Force Reserve JAG colonel – is seen as a logical successor for Mattis. Graham is smart and well respected in defence circles. After the midterms, the public wounds from the Kavanaugh hearings may well have healed – or at the least the blame may no longer be laid at Graham’s feet. The core Trumpers also now see Graham as one of theirs.

If Graham is confirmed as Secretary of Defense, enter: Nikki Haley. Is it a coincidence that Senator Graham was one of the first senators to issue a statement praising Ambassador Haley following her resignation? Graham’s term would not be up until 2020 and Senator Haley would be a coup for Republicans, who need more high profile, well-respected women. She's a logical replacement. 

Such an appointment would allow Haley to step out from under the directives of President Trump and perhaps, more importantly, the heavy hand of National Security Advisor John Bolton, who himself was a former US ambassador to the UN. 

As a popular former governor of South Carolina, Haley shouldn’t have any trouble getting re-elected when the time comes. With higher ambitions clearly in her sights, she would be in a much better position for a 2024 presidential run as Senator Haley, rather than Ambassador Haley.