President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Monday marked chief of staff John Kelly John Francis KellyMORE's one-year mark at the White House, which comes amid speculation he could soon leave his post.

Trump acknowledged Kelly's work anniversary during a swearing-in ceremony for the new Secretary of Veterans Affairs, Robert Wilkie.

"One year today, right? He became my chief of staff, Gen. Kelly," Trump said in the Oval Office. "John Kelly. In case of anybody's never heard of him."

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The president later mentioned his top aide's service on Twitter with a photo of the two men smiling and standing side by side.

Congratulations to General John Kelly. Today we celebrate his first full year as @WhiteHouse Chief of Staff! pic.twitter.com/JWCaJ3GhHV — Donald J. Trump (@realDonaldTrump) July 30, 2018

Kelly, who was the Homeland Security secretary prior to his appointment to the White House, was brought into the West Wing last summer to replace ousted chief of staff Reince Priebus Reinhold (Reince) Richard PriebusLeaked audio shows Trump touted low Black voter turnout in 2016: report Meadows joins White House facing reelection challenges Trump names Mark Meadows as new chief of staff MORE and impose order on a chaotic staff that was riven by internal divisions.

The former Marine Corps general succeeded in imposing some changes, such as limiting who could meet with the president, but eventually saw his stature decline as Trump bucked his efforts to implement greater control.

The chief of staff also suffered damage for his handling of spousal abuse allegations against former White House staff secretary Rob Porter, who was a key Kelly ally.

Kelly, who is said to have set a goal of lasting one year in the job, has been rumored to be on the way out of the White House. But it is unclear if his departure is imminent and whom Trump might pick to replace him.

Office of Management and Budget Director Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE and Nick Ayers, chief of staff to Vice President Pence, have been under consideration as possible replacements for Kelly.