Secretary of the Army Mark Esper is officially going through the confirmation process to become Secretary of Defense this week — finally bringing a Senate-confirmed official to the Pentagon’s top spot after nearly seven months. Former Secretary Jim Mattis left in January.

Esper, a former top lobbyist for Raytheon and Army officer, had already been serving as Acting Defense Secretary since June 24. He handed those duties over to Navy Secretary Richard Spencer Monday afternoon once the White House made his nomination official. (No, not that Richard Spencer.)

In those three weeks, he’s represented the US at a meeting of NATO defense ministers where, in the midst of a tense standoff between the US and Iran, he pressed America’s European allies to take a harder stance against Tehran.

He’ll likely face questions about the US’s approach to that Middle Eastern country and the broader region Tuesday — not to mention some grilling from Sen. Elizabeth Warren (D-MA) about his defense industry past and any possible conflicts of interests it could pose.

But his nomination is expected to move quickly: The Pentagon has been without a permanent defense secretary for much longer than Esper’s been running the ship. Former Deputy Defense Secretary Patrick Shanahan had been overseeing America’s annual $700 billion military enterprise since Mattis’ resignation and was expected to be nominated initially. That came to an abrupt end in mid-June, as Vox’s Jen Kirby explained:

While Trump indicated Shanahan wanted to “devote more time to his family,” his announcement coincided with reports of past domestic disputes, which the FBI had been examining as part of Shanahan’s background check, according to USA Today. … These incidents were not made public when Shanahan was confirmed as the No. 2 at the Pentagon in July 2017, but Shanahan reportedly faced an unusually long FBI background check for the secretary role. This, combined with other questions about Shanahan’s qualifications for the role and some reticence among lawmakers, may have ultimately derailed his nomination.

The resulting turmoil has left the Pentagon without a confirmed defense secretary — not to mention other vacancies at its top levels — amid escalating tensions with Iran and ongoing conflicts in the Middle East.

Mark Esper, briefly explained

Esper, a West Point graduate, served in both the Army and National Guard, but before becoming the Army’s top civilian leader in November 2017, he was perhaps best known in Washington for the seven years he spent as Raytheon’s top lobbyist.

After spending more than a decade on active duty, Esper served as a deputy assistant secretary of defense in the George W. Bush administration and a policy director for the House Armed Services Committee before working for the US Chamber of Commerce and the Aerospace Industries Association and eventually joining Raytheon.

As Army secretary, Esper worked on personnel reform and focused on acquiring new weapons for a “high-intensity conflict” with countries like China or Russia.

But that recent defense industry background could cause him some trouble at his confirmation hearing. Warren, a 2020 contender who’s questioned many of Trump’s Pentagon nominees with ties to the military industrial complex, warned Esper on Monday that he would have to “clear any ethics cloud” from his time with one of America’s largest defense contractors. She has already released a plan calling for a ban on the well-established revolving door between defense contractors and the Pentagon.

But even so, he’s garnered praise from both sides of the aisle and was confirmed to his current spot nearly two years ago by an 89-6 vote. If he sees a speedy confirmation vote — and it could come as early as Thursday — he will be far from the first of Trump’s nominees to be confirmed despite senators’ concerns about his industry connections. He would join Shanahan before him, not to mention recently departed Air Force Secretary Heather Wilson and several others. In fact, as the Wall Street Journal’s Vivian Salama, Gordon Lubold and Nancy Youssef note, Trump has increasingly turned away from “the generals”:

After President Trump took office, he frequently lauded “my generals” and installed several top military figures in prominent roles. But since then, often after friction over policy and personality, those men have moved on, and Mr. Trump has become less enamored of the appointment of those with military careers, according to people familiar with the matter. Mr. Esper’s appointment would mean there are no longer any senior military personnel — or recently retired generals — in the administration’s top ranks of permanent officials outside of Gen. Joe Dunford, the chairman of the Joint Chiefs of Staff, the president’s senior military adviser. Mr. Dunford was appointed to his four-year term by President Obama in 2015.

It’s been a bumpy 2019 for the Defense Department leadership

When James Mattis resigned at the start of the year — over a disagreement with Trump about US policy in Syria — it kicked off an unprecedented half year of volatility at the top levels of the Pentagon.

Shanahan, then deputy defense secretary, stepped into the lead spot in an acting capacity. For months, Trump said his nomination would be sent to the Senate any day. But last month, as pushback to the nomination from senators was already growing, news broke about past domestic incidents that had raised red flags. Here’s Vox’s Kirby again on a few of them:

At least one of the incidents involved Shanahan and his ex-wife, both of whom accused the other of punching them in an August 2010 incident. Shanahan’s ex-wife was arrested after the incident, though charges were later dropped. Shanahan denied the allegations that he assaulted his ex-wife to both USA Today and the Washington Post. In another disturbing incident reported by the Post, Shanahan defended his 17-year-old son who allegedly beat his mother with a baseball bat.

Esper took over as acting head, but his move and the double vacancy caused by Shanahan’s resignation — not just from the acting SecDef role, but from his confirmed deputy position as well — meant a number of other civilian military leaders were shuffled around.

And once Esper’s nomination was sent to the Senate, he legally couldn’t serve as the acting chief anymore. Cue Navy Secretary Spencer stepping in. If you’re counting, as the AP’s Robert Burns did, that’s meant three different acting secretaries have held the Defense Department reins this year alone:

Prior to the Trump administration, only twice before has the Defense Department been led by an acting secretary — most recently in 1989 — and never has it had more than one in a single year.

To deal with all those vacancies, the Trump administration has been playing a game of musical chairs with its civilian military leadership. Assuming Esper is confirmed on Thursday, here’s what happens next — just on Thursday. Per NBC’s rather comical timeline of rotating characters this week to achieve an official confirmation:

When Esper is sworn in, Richard Spencer will stop being acting defense secretary and will revert to his previous job, secretary of the Navy. Ryan McCarthy will resume his position as acting secretary of the Army.

Then, the following week, again from NBC:

David Norquist will be formally nominated to become deputy secretary of defense, the second most powerful position at the Pentagon. Upon his nomination, Norquist, who had been acting deputy of secretary of defense, will revert back to his previous job, comptroller. While Norquist awaits confirmation, Under Secretary of Defense for Acquisition and Sustainment Ellen Lord will become acting deputy secretary of defense. It will be only the second time a woman has held this position.

This all comes at a precarious time — the US’s longstanding “special relationship” with the United Kingdom is increasingly fraught after the British ambassador to the US resigned after cables leaked in which she called Trump “inept,” tensions with Iran have only increased since the US withdrew from a negotiated nuclear deal last year, and the war in Afghanistan is only a few months from adulthood.

A confirmed defense secretary is, at least, step one to reassuring those allies and guiding the US military in its numerous overseas engagements.