WASHINGTON (AP) - President Donald Trump is weighing an administration-wide shakeup as he looks to prepare his White House for divided government, but it is unclear who is going and who is staying.

Homeland Security Secretary Kirstjen Nielsen was thought to be out as soon as this week, according to two people with knowledge of the issue, but she is now likely to remain in the post for a longer period because there is no obvious successor in place.

Trump has soured on Nielsen and White House chief of staff John Kelly, in part over frustration that his administration is not doing more to address what he has called a crisis at the U.S.-Mexico border, according to the two people. But the scope of the contemplated changes is far broader, as Trump gears up for a wave of Democratic oversight requests and to devote more effort to his re-election campaign.

According to people familiar with the situation, Trump is also discussing replacing Kelly with Vice President Mike Pence's chief of staff, Nick Ayers. Kelly, a retired Marine general, has been credited with bringing order and process to a chaotic West Wing, but he has fallen out of favor with the president as well as with presidential daughter Ivanka Trump and son-in-law Jared Kushner.

Ayers, a seasoned campaign operative, would restore a political mindset to the role, but he faces stiff opposition from some corners of the West Wing, with some aides lobbying Trump directly against the move.

Other changes are afoot, as Commerce Secretary Wilbur Ross and Interior Secretary Ryan Zinke are being discussed for replacement. And in an extraordinary move Tuesday, first lady Melania Trump's office called publicly for the firing of Trump's deputy national security adviser, Mira Ricardel.

For all the talk of churn, Trump often expresses frustration with aides and then does not take action. Talk of Kelly's exit has percolated for months, and he remains in place.

Nielsen had hoped to complete one year in the job and leave in December, but it appeared unlikely she would last that long, said two people with knowledge of the debate. They spoke to the AP on condition of anonymity because they were not authorized to speak publicly.

Curbing illegal immigration is Trump's signature issue - and one he returns to as a way to rally his most loyal supporters.

But anyone who takes over at Homeland Security is likely to run up against the same problems that Nielsen faced. The administration has already tried to clamp down at the border, but those efforts have been largely thwarted or watered down because of legal challenges.

Trump also told allies that he never fully trusted Nielsen, whom he associated with President George W. Bush, a longtime foe. And he told those close to him that he felt, at times, that her loyalty was more toward her longtime mentor - Kelly - than to the president.

Zinke, who faces several ethics investigations, said in an AP interview on Monday that he has spoken in recent days with Trump, Pence and Kelly about probes into his leadership and they remain supportive. He denied any wrongdoing.

Ross addressed turnover rumors at a Yahoo Finance summit Tuesday, saying he was in the post to give back to the country and support Trump.

"I worked very hard to get President Trump elected," he said. "Now I'd like to work equally hard to have him succeed and be re-elected."

Questions about Nielsen's job security are not new. Earlier this year, she pushed back on a New York Times report that she drafted a resignation letter after Trump scolded her at a Cabinet meeting, but did not submit it.

Nielsen has led the sprawling post-Sept. 11 federal agency since December. She had been chief of staff to Kelly when he was Trump's first Homeland Security secretary. A DHS spokesman would not comment on whether she was leaving.

"The secretary is honored to lead the men and women of DHS and is committed to implementing the president's security-focused agenda to protect Americans from all threats and will continue to do so," spokesman Tyler Houlton said.

Nielsen advocated for strong cybersecurity defense and often said she believed the next major terror attack would occur online - not by planes or bombs. She was tasked with helping states secure elections following interference by Russians during the 2016 election.

She pushed Trump's immigration policies, including funding for his border wall, and defended the administration's practice of separating migrant families, telling a Senate committee that removing children from parents facing criminal charges happens "in the United States every day." But she was also instrumental in stopping the separations.

Just last week, the administration announced that migrants would be denied asylum at the U.S.-Mexico border if they crossed illegally, creating regulations that circumvent immigration laws stating anyone can claim asylum no matter how they arrive to the country. The decision would affect about 70,000 people annually and was immediately challenged by the American Civil Liberties Union.

Nielsen also moved to abandon long-standing regulations that dictate how long children are allowed to be held in immigration detention, and she requested bed space from the U.S. military for some 12,000 people in an effort to detain all families who cross the border. Right now there is space for about 3,000 families, and it is at capacity.

She got into heated discussions with Trump and White House aides several times over immigration policy as she sought to explain the complicated legal challenges behind immigration law and pushed for a more diplomatic approach.

It's unclear who would replace her. The job requires Senate confirmation, and there is no deputy secretary. Under Secretary for Management Claire Grady would be the acting head if Nielsen left.

Associated Press writers Darlene Superville in Washington and Jonathan Lemire in New York contributed to this report.