In a wide-ranging interview on Sunday morning, acting chief of staff Mick Mulvaney told host Chris Wallace of “Fox News Sunday” that the White House is “very close” to identifying the person or persons who leaked the president’s White House schedule to Axios last week.

“Someone within the White House spent three months collecting this information, which is really, really hard to do,” said Mulvaney. “And it also sheds light on the fact that many people who work for us weren’t hired [by] us.”

“We need civil service reform so the president can trust everyone working for him, and we’re not there right now,” Mulvaney also said.

About 400 individuals receive the material in leaked memos, according to Mulvaney, who described the content as “not that confidential.”

President Donald Trump himself weighed in on this issue on Sunday, in two tweets:

Mulvaney added Sunday morning on “Fox News Sunday” that as acting chief of staff, he receives “much more private schedules.”

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He also hinted the culprit or culprits are likely “career staffers” — and he zeroed in on civil service protections that can hamstring new administrations.

He said his time working with the Consumer Financial Protection Bureau showed him that it is “nearly impossible to fire a federal worker.”

When Wallace asked Mulvaney how close they were to finding out who leaked the memos, Mulvaney replied, “We’re hoping to have a resolution on that this week.”

Related: Mulvaney on the Shutdown: It’s Democrats Who Won’t Allow It to End

Mulvaney also addressed the ongoing impasse over funding for President Trump’s proposed security wall on the southern border.

“This wall is going to get built with or without Congress,” said Mulvaney. “We’ll take as much money as [Congress] can give us and then we will go off and find the money someplace else, legally, in order to secure that southern barrier,” he added of the administration’s current attitude regarding the negotiations.

Mulvaney said congressional Democrats, in his estimation, “don’t … know where they stand on this particular issue,” and added that he had heard proposals ranging from zero to $2.6 billion.

He also said a government shutdown is “technically still on the table,” as is declaring a national emergency.

Funds are legally available to the president, he emphasized, through “reprogramming,” should the proposed bill — as seems likely — fall short of what the president needs, which Mulvaney said is “well north of $5.7 billion.”

Related: Border Wall Construction Set to Begin in Rio Grande Valley, Texas, Very Soon

Some of those funds to make up the difference, he explained, are available without a government shutdown, while other sources would require one.

Mulvaney also warned the president could refuse to sign a bill based on content within it unrelated to the wall.

“He would prefer legislation because it’s the right way to go and is the proper way to spend money in this country. But if that doesn’t happen, the president proceeds. His number-one priority is national security. He will then look at the National Emergencies Act as a way to do his job.”

Later in the show, bipartisan conference committee member Richard Shelby (R-Ala.) said “talks are stalled right now,” adding his hope is that a compromise can be reached later on Sunday or on Monday morning.

Shelby pointed specifically to a current sticking point involving the Democrats’ desire for a cap on Immigration and Customs Enforcement (ICE) detaining criminals coming into the United States.

Fox News chief congressional correspondent, Mike Emanuel, noted a deal must be struck by Monday for the compromise to pass through the House and Senate by the end of the week.

Emanual added that Democrat sources have signaled the potential deal on the table for physical border barriers falls well short of president Trump’s $5.7 billion ask — that it’s somewhere between $1.3 billion and $2 billion.

Also, Mulvaney and Wallace engaged in a friendly verbal tussle over President Trump’s remarks during the State of the Union address last Tuesday night in which the president targeted the “ridiculous, partisan investigations” he believes are, in part, to blame for Congress’ failure to do its job on behalf of the American people.

“It’s not reasonable to expect the president to work with you on Monday on a big infrastructure bill and then on Tuesday have you punch him in the face over 15 different investigations,” said Mulvaney.

“You can’t do both,” Mulvaney added of congressional Democrats. “You can’t go home and tell the voters back home that you’re going to work with the president — and then come to Washington and do nothing but investigate the president.”

See these tweets — then check out the video down below:

Check out this video:

Michele Blood is a Flemington, New Jersey-based freelance writer and regular contributor to LifeZette.