WASHINGTON — President Donald Trump isn’t committing to a previous pledge to keep chief of staff John Kelly for the remainder of his term, part of widespread speculation about staffing changes that could soon sweep through his administration. Trump, in a wide-ranging interview that aired on “Fox News Sunday,” praised Kelly’s work ethic and much of what he brings to the position but added, “There are certain things that I don’t like that he does.” “There are a couple of things where it’s just not his strength.