President Donald Trump said on Friday that he gets along well with his embattled White House chief of staff but doesn't know how long John Kelly will remain in the job.Kelly has been back in the spotlight this week as word surfaced that the president has been sounding out allies about potential replacements for the retired four-star general. Kelly is credited with bringing order to the West Wing but also grates on the freewheeling president.Asked about all the speculation, Trump told reporters aboard Air Force One that "we're getting along very well". But he added: "Look, at some point, things happen but I will tell you ... we have a very good relationship. He's a wonderful man."Asked if Kelly was leaving, the president said, "That I don't know. I like John a lot. I like him and I respect him." The president spoke en route to a weekend at his golf club in New Jersey.Two possible replacements for Kelly: Trump's budget director, Mick Mulvaney, and Vice President Mike Pence's chief of staff, Nick Ayers, according to two people with knowledge of Trump's thinking. The sources spoke on condition of anonymity because they were not authorised to discuss personnel matters.Trump often openly muses about replacements for his aides without follow-through, and speculation has bubbled up about Kelly and other aides in the past without action.The White House has previously denied talk of impending staff shake-ups that later came to pass. The long list of White House staffers who have recently left or are planning to go in the coming weeks includes legislative director Marc Short.Kelly has told confidants he currently has no plan to leave and has made no formal preparations to do so, according to one person with knowledge of his thinking. But he has also told people close to him that he'd be happy if he made it to the one-year mark in the position, which would mean he stays until late July.The latest speculation about Kelly comes as he has seen his White House role diminished in recent months.Trump and Kelly have drifted apart, as the president has chafed at the retired general's attempts to impose order. The president has increasingly followed his own counsel and added more like-minded aides to his staff, many of whom have direct access to the Oval Office without going through Kelly.That list will soon include former Fox News executive Bill Shine, who is expected to join the administration as deputy chief of staff for communications.Kelly has often joked publicly about how working for Trump is the hardest job he's ever had, including those on the battlefield.Trump has discussed replacing Kelly before, and any personnel changes should be considered tentative until he carries them out. Rarely does the president directly fire anyone, frequently letting out-of-favour aides dangle in limbo for months.Mulvaney on Friday told Fox Business Network he'd "heard those same rumours about three times now in the last 12 months. I'll start dealing with that issue when the president actually raises it with me as opposed to the meeting that hasn't happened yet." Ayers did not immediate respond to a request for comment.Trump, fielding questions from reporters en route to a weekend getaway to his New Jersey golf course, suggested it's possible that Hope Hicks — who was a top campaign and White House aide before leaving in March— could someday return. "I'll bet you Hope misses it. I think everybody misses it.""You exhaust a lot of people, you understand that? You people exhaust a lot of people. They come in full of life and vim and vigour and they're exhausted and then they get their breath," Trump told reporters."And frankly Hope is great and so are many of the other people. Many people would like to come back. Look, there is nothing more exciting than what we're doing."