WASHINGTON — The White House is strongly considering Chad Wolf, the acting undersecretary for strategy at the Department of Homeland Security and former chief of staff to then-Secretary Kirstjen Nielsen, to head DHS, according to four current and former department officials familiar with deliberations on the matter.

Wolf is not considered as hard-line on immigration as two other names floated for the job — acting Director of U.S. Citizenship and Immigration Services Ken Cuccinelli and acting Commissioner of Customs and Border Protection Mark Morgan — but internal emails obtained by NBC News show Wolf was an early architect of the migrant family separation policy at the southwest border.

As far back as December 2017, when Wolf was acting chief of staff to Nielsen, he sent a list of 16 options to curb the number of undocumented immigrants to Gene Hamilton, counselor to then-Attorney General Jeff Sessions, for review.

Number two on the list: "Separate family units."

"Announce that DHS is considering separating family units, placing the adults in detention and placing minors under the age of 18 in the custody of HHS as unaccompanied alien children," Wolf wrote, referring to the Department of Health and Human Services, the agency that would later be called on to shelter more than 2,800 children separated from their parents in 2018.

Also included on the list were policies that would speed up the deportation of children (which has not come to pass) and require immigrants to seek asylum in Mexico (which has since been announced).

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The emails, first obtained by Democratic Sen. Jeff Merkley's office, were reported by NBC News earlier this year, but Wolf's name was not included in the report because he was not then being considered for a Cabinet level position, as he is now.

Wolf later served as chief of staff to Nielsen during the family separation policy, known as "zero tolerance," in May and June of 2018. Trump ended it through executive action in late June, after public outrage mounted and recordings emerged of migrant children crying for their parents behind chain-linked barricades.

Sources inside the administration, however, remain divided on Wolf and his ability to lead DHS in a manner tough enough to win the approval of the president and his senior adviser Stephen Miller.

One DHS official told NBC News that Wolf is "not a true believer" and has long billed himself as someone who leaves the policy decisions to others.

"He's mainly a process guy and played that part to a T as chief of staff to Nielsen," the official said. "Substantively, he's an aviation security type with some high-tech related immigration experience. His experience that lines up with [Trump's] agenda, particularly on border issues, was cobbled together from working for Nielsen."

A senior DHS official defended Chad’s record at the agency, describing him as "a proven leader consistently entrusted with tackling some fo the most complex security challenges of our time."

"There’s been no one more committed to the DHS mission and the president’s agenda than Chad, who’s helped implement the policies credited to addressing record levels of illegal crossings at the border," the senior DHS official said.

During his confirmation hearing in June for his current position as under secretary for strategy, policy and plans at DHS, Wolf was asked if he had concerns with the family separations policy.

Wolf responded: "My job was not to determine whether it was the right or wrong policy. My job at the time was to ensure that the Secretary had all the information that [Nielsen] needed."

Another U.S. official said Wolf is not as hard-line as someone like Cuccinelli on immigration and is seen as being aligned with Nielsen, who Trump blamed for the spike in undocumented immigration seen earlier this year.

Another U.S. official who worked with Wolf said he is well-respected within the Trump administration despite his close ties to Nielsen, who was ousted this spring, and is liked by Miller.

Wolf’s close working relationship with Miller has developed over the past year and may help him should he be tapped to run the agency, the sources said. But one official said there is concern that the role is too big for Wolf. While he might not push back on the administration’s goals for immigration, he is seen as a temporary placeholder, not as someone who would be nominated to be confirmed by the Senate.

Former Homeland Security Secretary Jeh Johnson, who served under President Barack Obama, said the Trump administration is forgetting how many other issues the head of DHS must address, not just immigration.

"I look at the current DHS with great despair and worry. We need a presidentially appointed, Senate-confirmed official in the job of protecting the homeland from the land, sea, air, at the ports, and in cyberspace," Johnson told NBC News. "Given this administration’s intense focus on the southern border, it is easy to forget all these other vital homeland security missions."

"The job is too big and too important to fill again with another 'acting' from somewhere within the ranks of DHS. A president who neglects for too long finding a nominee for the job is himself neglecting his duty to protect the homeland."

DHS did not respond to a request for comment.

From DHS to lobbying and back again

Wolf first came to DHS in its early days, overseeing the creation of the Transportation Security Administration as the agency's chief of staff just after the Sept. 11, 2001, attacks.

He then worked for Wexler & Walker, a now-defunct Washington lobbying firm, for 11 years, where he helped secure contracts from TSA on behalf of his clients.

Wolf is considered the current front-runner for the job in large part because Cuccinelli and Morgan have been deemed ineligible due to rules governing federal vacancies that mandate acting officials must have served at least 90 days in the past year under the previous secretary. Because Nielsen was the last Senate-confirmed secretary and Cuccinelli and Morgan did not serve under her, they are deemed ineligible. The Wall Street Journal was first to report that White House personnel director Sean Doocey relayed this information to the president on Monday.

Others considered for the position include David Pekoske, the current administrator of the Transportation Security Administration and acting deputy secretary of DHS, and Chris Krebs, the director of DHS's Cybersecurity and Infrastructure Security Agency.

The current acting secretary of DHS, Kevin McAleenan, recently notified the White House that he would be leaving the job on Oct. 31 or at another date chosen by Trump.

It is not known whether Wolf would be nominated to the Senate to be confirmed as DHS secretary or whether he would temporarily fill the spot until another candidate is chosen.