In four years, President Donald Trump went through four National Security Advisors. The last of these, Robert C. O'Brien, may have been the best fit.

Prior to the current occupant of the White House, O'Brien has served in every administration of the 21st Century, including Barack Obama's. A diplomatic professional, he also advised the presidential campaigns of Mitt Romney, Scott Walker and Ted Cruz.

In this, the silly season of politics before the midterms, some are talking up the former ambassador as a possible 2024 contender - but, of course, all speculation is done under the shadow of Trump who is considering his own comeback bid.

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