Transcript for John Kelly set to leave the White House

President trump revealing his chief of staff, John Kelly, is leaving by the end of this month. The departure of the retired marine, four-star general, once tasked with bringing order to the oval office. ABC's David Wright is at the white house with more. Reporter: En route to the army-navy game, president trump announced the west wing is losing a key player. John Kelly will be leaving. I don't know if I can say retiring. But, he's a great guy. John Kelly will be leaving at the end of the year. Reporter: Chief of staff John Kelly's marching orders were to bring some discipline to a chaotic white house staff. He will do a spectacular job, I have no doubt, as chief of staff. Reporter: He's had mixed success. Kelly fired omarosa Manigault in the white house situation room, an encounter she secretly recorded. Hi. I'm only going to stay for a couple of minutes. These are lawyers. We're going to talk to you about leaving the white house. Reporter: He's clashed openly outside the oval office with John Bolton over immigration issues. An altercation with Corey Lewandowski reportedly got physical. Some members of trump's inner circle bristled at Kelly's efforts to limit direct access to the president, and trump clearly doesn't like to be managed. Look, we get along well. There are certain things I love what he does. And there are certain things that I don't like that he does. Reporter: When he first took on the chief of staff job, Kelly joked that it wasn't exactly his first choice assignment. But I did something wrong and god punished me, I guess. Reporter: But duty called, and Kelly stepped up. Kelly was reportedly planning to announce his departure Monday. But today, president trump stole his thunder. We'll be announcing who will be taking John's place. It might be on an interim basis. All right, David joins us now from Washington. On that point, David, what are we learning tonight about possible successors to Kelly? Tom, we're told the front runner is likely to Nick ayers, 36 years old, considered a political whiz kid. Currently serving as Mike pence, the vice president's chief of staff. Tom. David Wright for us tonight, thank you.

This transcript has been automatically generated and may not be 100% accurate.