Chuck Hagel was a Barack Obama mentor, which made him part of the president's inner circle. But when the defense secretary drifted, he had to leave. And so it goes in Barack Obama's war cabinet.

When Obama announced Hagel's departure on Monday, it added fuel to a debate among lawmakers and insiders about what many see as a White House — and a president — that lacks trust in the national security apparatus.

In the wake of a scandal involving then-CIA Director David Petraeus and his mistress, Obama sent an inner circle stalwart, then-National Security Adviser John Brennan, to replace him. When Obama needed a trusted treasury secretary to follow Tim Geithner, he turned to his then-chief of staff, Jack Lew.

Even Hagel, who schooled then-Sen. Obama on national security and foreign policy matters during a 2008 trip to war-torn Iraq, was deployed to the Pentagon as Obama's hand-picked reformer.

But it was a lesser-noticed move — the Nov. 7 nomination of Principal Deputy National Security Adviser Tony Blinken to be deputy secretary of state — that got the attention of lawmakers and experts. The post is typically held by a career diplomat.

"They have this need to control every message that gets out," said Rep. Ileana Ros-Lehtinen, R-Fla., a former House Foreign Affairs Committee chairwoman. "And to appoint somebody who's more political than a diplomat, it just means you want more control over the message you're sending out."

Incoming Senate Armed Services Committee Chairman Sen. John McCain, R-Ariz., in a Monday statement about Hagel's resignation, referenced other former national security officials' descriptions of a controlling White House.

Ros-Lehtinen said she agrees with the characterization of a White House that micromanages the national security agencies.

"They want every statement … to be cleared," she said. "And they want someone that they can trust."

'Circling the Wagons'

Trust became an issue with Hagel, according to sources and reports, as the White House — including Obama — developed a deficit of it in their Pentagon boss.

"Hagel was starting to push back," said one defense lobbyist with ties to Capitol Hill. "Decisions were made without him or his senior people at DoD on [the Islamic State] and Ebola.

"Hagel's been battling with them behind the scenes," the lobbyist added, referring to White House officials.

In an interview last week, Senate Armed Services Committee member Sen. Lindsey Graham, R-S.C., said he thinks recent high-level appointments and moves show the White House is "looking for as much compliance as they can find."

"I think, yeah, they're very much circling the wagons," Graham added.

Larry Korb, a senior member of Obama's 2008 campaign, said "there's no doubt" Obama and the White House have a trust deficit with the Pentagon and other security agencies.

"I think that hurts policymaking," Korb said. "I really do. I think Obama probably was dumbfounded when he came into office … that everyone in the government didn't do what he wanted right away. … So the reaction is to look for Obama loyalists."

Aaron David Miller, an adviser to six secretaries of state and now vice president of the Wilson Center, said of Obama: "He dominates [and] doesn't delegate."

"I'm sure the circle-the-wagons mentality is part of that," Miller said. "[Obama] is probably the most controlling foreign policy president since Richard Nixon."

'Very Insular'

Asked on Nov. 18 if he believes the White House lacks trust in outside figures, Senate Foreign Relations Committee Ranking Member Sen. Bob Corker, R-Tenn., replied: "Sure."

"I've asked those same questions privately," Corker said. The following day, during Blinken's confirmation hearing, Corker expressed concerns in public.

During the hearing, Corker said Obama has been "very insular" by sending members of his inner circle to hold senior government posts. Corker even bluntly told Blinken, if he is confirmed, "don't spin for the White House."

Blinken responded by saying, if confirmed, he would "advocate strongly for the State Department" and "help move [the policy] process forward."

On Monday, the White House said it was Hagel who first brought up the notion that he should step down.

"In October, Secretary Hagel began speaking with the president about departing the administration given the natural post-midterms transition time," National Security Council spokeswoman Bernadette Meehan said in a statement. "Those conversations have been ongoing for several weeks."

Last week, several Democratic members, including Senate Armed Services Committee member Sen. Claire McCaskill of Missouri, shot down any notion of a micromanaging White House that doesn't trust the national security and foreign policy realm.

"No," McCaskill said during a brief interview. "I think that's maybe a stretch."

SASC Chairman Carl Levin, D-Mich, who has observed many administrations during his three-decade Senate career, said he "wouldn't read [mistrust] into it."

"I think it shows their confidence in Tony Blinken," Levin said.

'Chuck was Frustrated'

Evidence mounted after Hagel's resignation that the president simply lost trust in the man he sent to lead the Afghanistan drawdown and manage military budget cuts — and vice versa.

McCain's statement revealed Hagel told him last week of his mounting frustrations with the White House.

Hagel, as his now infamous leaked memo to National Security Adviser Susan Rice showed, disagreed with Obama's plans for fighting the Islamic State group and other aspects of his approach to global threats.

"I know that Chuck was frustrated with aspects of the administration's national security policy and decision-making process," McCain said.

That frustration added to the mistrust. Hagel was out of the inner circle. He had to go.

Obama's other defense secretaries, Robert Gates and Leon Panetta, "didn't toe the party line, so the White House people weren't happy," Korb said. "So pushed out is what they got. Now, this is what Hagel got, too."