As President Donald Trump looks to reshape the executive branch, he's avoiding the words "You're hired."

Trump's choice of Kevin McAleenan as acting replacement for Homeland Security Secretary Kirstjen Nielsen spotlights the president's increasing reliance on a once-obscure federal statute that governs how to fill vacant federal posts. It also raises fresh questions about his reliance on temporary appointments for key security roles. The reality-star president, who once made staff churn into prime-time television, has overseen massive turnover in just two years in office. But he's shown little concern for creating uncertainty about the leadership of some of the country's most important agencies.

Disordered departures have become the rule in the Trump administration, with aides and even Cabinet officials pushed out at a record pace, often with no clear replacement plan in place. And when he does have a plan, Trump has made a habit of taking the creative route, going around in-place deputies to select other officials he believes are more loyal or amenable to his agenda.

Officials with "acting" titles abound in key roles, from the secretary of defense to the U.S. ambassador to the United Nations, and even the White House chief of staff. And when Linda McMahon's resignation as Small Business Administrator takes effect later this week, that agency will be led by yet another acting official. Trump has announced his intention to nominate Jovita Carranza, the current treasurer of the United States, for the role.

The Federal Vacancies Reform Act of 1998 gives a president wide berth to fill openings across the executive branch and he's used it without restraint to re-jigger the succession plans of the Departments of Justice and Veterans Affairs. But in selecting McAleenan, Trump will have to go even further. The agency's undersecretary of management, Claire Grady, is technically next in line for the job. She will need to resign — or more likely be fired — in order for McAleenan to assume the acting position under the act.

Allowing individuals to fill roles in an acting capacity allows the White House to avoid Senate confirmation battles. Trump has seen several high-profile nominations founder, and others that have become distracting political fights.

"I like acting. It gives me more flexibility. Do you understand that?" Trump said in January, facing questions about acting chief of staff Mick Mulvaney and acting Defense Secretary Patrick Shanahan. "I like acting. So we have a few that are acting. We have a great, great Cabinet."

But it also serves as a "run around Congress," said the Brookings Institution's Darrell West. "He's worried that he would not be able to get all of these people through the U.S. Senate, even though Republicans still control the Senate."

West added: "It makes the administration look chaotic and not really in control of what it is doing, but Trump seems comfortable with that and he seems willing to live with that reality."

White House officials acknowledged that the roster of "actings" was not ideal, saying Trump's haste to make personnel changes, even without establishing succession plans, reflected his experience in the private sector. Some suggested it marked Trump's wariness to hire the wrong people.

But the president has struggled to attract top-tier talent since even before taking office, in part because he has maintained a loyalty test that has kept away many qualified Republicans who were critical of his candidacy during the presidential campaign.

Shanahan assumed the post in December after Defense Secretary Jim Mattis resigned over the president's Syria withdrawal plans and Trump has not named a permanent replacement. Mulvaney has been acting in the role since January, after the departure of chief of staff John Kelly.

At the Interior Department, David Bernhardt is serving in an acting capacity while his nomination to fill the role full time is pending before the Senate. The Office of Management and Budget is led by Russell Vought, while Mulvaney is at the White House.

"White House jobs and administration jobs are uber temporary because they're very difficult," said Matt Schlapp, a White House ally and chairman of the American Conservative Union. That's especially true for those who work for a Republican and especially Trump, Schlapp added, citing negative press and heightened media scrutiny.

Additional "actings" fill posts at the sub-Cabinet level.

Trump last week suddenly rescinded the nomination of acting Immigrations and Customs Enforcement director Ron Vitiello to lead the agency permanently. And the Federal Aviation Administration has been led by an acting administrator, Daniel Elwell, since January 2018. Trump didn't nominate a permanent replacement until last month in the wake of a pair of aviation disasters.

The Senate Judiciary Committee's top Democrat, Sen. Dianne Feinstein of California, said at the Homeland Security Department alone at least 10 top positions are filled in an acting capacity.

"The purge of senior leadership at the Department of Homeland Security is unprecedented and a threat to our national security," she said.

On Capitol Hill Trump's use of acting officials has drawn scrutiny from within his own party as well, both over concerns that Trump was usurping their authority and that the instability could make the nation less safe.

"I don't know what his rationale is, but it's bound to create more challenges," said Texas Sen. John Cornyn, the number two Republican in the chamber. "They're not subject to Senate confirmation when they're in acting, and I think we need some more certainty, more predictability would be good."

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AP writers Jill Colvin, Lisa Mascaro and Tracy Brown contributed.