White House aides have been informed they must decide before the end of the month whether they will stay with the administration through the 2018 midterm elections in November, according to a report Tuesday.

White House chief of staff John Kelly is working to fill positions before January ends, mitigating the flow of outgoing advisers, CNN reported. However, a lack of qualified and willing replacements, coupled with a long hiring process, is complicating the effort.

Some officials who may soon be on their way out include White House counsel Don McGahn and national security adviser H.R. McMaster — two people Trump has vented about publicly. However, their future at the White House is not yet decided, the report said.

McMaster, an active duty three-star general, has been at odds with Trump concerning policy in Afghanistan and Iran, while McGahn has a compelling legal reason to stay since he is a potential witness in special counsel Robert Mueller’s Russia probe, a source familiar with the situation told CNN.

Gary Cohn, the National Economic Council chairman, is still deciding on his future at the White House, according to the report. Although his departure has been discussed since August, he claimed on Saturday that he is “happy” with his job when called up on stage by Trump during a media availability.

Dina Powell, deputy national security adviser, announced she would leave her post last year. However, she intends to stay active with senior adviser Jared Kushner’s Middle East efforts and will accompany Vice President Mike Pence to the Middle East next week.

Departing aides or those who are anticipated to depart include deputy chief of staff Rick Dearborn, Cohn’s deputy at the National Economic Council Jeremy Katz, and Sean Cairncross, who Trump nominated to oversee the Millennium Challenge Corporation.

Omarosa Manigault-Newman was ousted from her position as communications director at the Office of Public Liaison late last year.