Stephen K. Bannon, the president’s chief strategist and one of his most controversial advisers, is exiting the Trump administration after a tumultuous seven-month stint. The White House released a statement Friday saying that Bannon and White House chief of staff John Kelly had “mutually agreed” that this would be Bannon’s last day in his job.

Bannon’s departure has been long in the making. Trump signaled his public displeasure with Bannon’s high media profile back in April, and the chief strategist’s clashes with other administration officials have only worsened since. A new round of rumors about Bannon’s potentially imminent departure began swirling after Kelly was named chief of staff in late July and began exploring how to restructure the dysfunctional West Wing.

Then Bannon poured gasoline on the fire by giving a shockingly candid interview to liberal journalist Robert Kuttner Tuesday, in which he criticized some of his rivals in the administration by name, contradicted Trump’s stated North Korea policy, and explained his plans to reshuffle State Department personnel.

This provided his many internal enemies — who had already accused him of being too eager to leak and to take internal disputes to the press — with several more reasons to call for his head. (Bannon’s allies have put out the word that he wasn’t aware his remarks would be reported, which seems rather sloppy of him.) Now, Bannon is claiming that his departure was his own idea, and that he submitted his resignation two weeks ago — but several reporters are hearing that he was in fact fired.

In any case, Bannon’s exit marks a major milestone for an administration and indeed a party that he’s influenced in profound ways. Bannon has attempted to steer Trump administration policy, and the GOP generally, toward what he dubs nationalism.

Part of this strategy involved stoking white voters’ resentments of various “others” — immigrants, Muslims, Black Lives Matter protesters — beyond what was previously considered acceptable by GOP elites. President Trump shares Bannon’s instincts, and so this resentment stoking has suffused much of Trump’s campaign and presidency (as we saw in the president’s statements on the violence in Charlottesville).

Much of this will surely continue despite Bannon’s departure. But in losing Bannon, Trump is losing an adviser who was deeply committed to implementing this agenda at a granular level — someone who cared about policy details and lower-level personnel appointments, rather than just presidential tweets or statements.

Furthermore, Bannon has said he wants to turn the GOP toward economic nationalism — which he defines as tougher trade policies, increased infrastructure spending, and perhaps even tax hikes on the wealthy — as well. But he’s been much less successful on that front, as other advisers and interests have argued in favor of Republican status quo policies on economic issues, and have mainly won out in the Trump administration so far.

Bannon wasn’t Trump’s brain. But they had similar passions.

While Bannon has often been characterized as the shadowy adviser whispering things to Trump — “Trump’s brain” — the truth is more complicated. Many of the signature characteristics of Trump’s politics predated August 2016, when Bannon joined Trump’s campaign as its CEO.

What actually happened was that in the years before Trump’s campaign, he and Bannon seemed to come to parallel but similar realizations about what much of the GOP base wanted and truly cared about — and weren’t getting from existing Republican elites.

For Bannon, this realization came through running the conservative media outlet Breitbart News and noticing which issues resonated most with readers: The site spotlighted tales of lurid crimes committed by unauthorized immigrants, Muslims, and African Americans. Trump was drawn toward the same sorts of rhetoric, from the moment he launched his campaign and denounced Mexico for sending “rapists” to the US.

“Both of them had a real talent for kind of stoking resentment and channeling that resentment into a political force that they could direct at more mainstream Republicans and at Democrats,” Josh Green, author of the book Devil’s Bargain, told me in July.

The two men also shared a disdain for the GOP establishment. They had little use for Republican orthodoxy on economic issues (Bannon and Trump are both harsh critics of recent multilateral trade deals), and for what they viewed as an overly politically correct approach to campaigning.

But where Trump mainly expressed his views in off-the-cuff remarks and sound bites, Bannon tried to stitch it all together in a grand theory. Trump and his voters, he said, were part of a “global populist movement” challenging the power and conventional wisdom of political, cultural, and business elites in favor of “nationalism.”

Bannon dominated the Trump administration’s earliest days — and then lost influence

So days after Trump unexpectedly won the presidency, he announced that Bannon would be his White House chief strategist — a newly created position given equal billing with Reince Priebus’s appointment as chief of staff.

Bannon’s appointment was massively consequential because of where he came from and whom he was most focused on satisfying — the Breitbart base. By naming Bannon his top political adviser, Trump was signaling that his top political priority would be pleasing that base, rather than reaching out to try to build broader support. That was, after all, what Bannon knew how to do.

Furthermore, there was a power vacuum during the chaotic transition period, and Bannon took advantage of it. He helped craft a series of executive orders Trump could use to start off his presidency with a bang, in a strategy deemed “shock and awe.”

Several of the orders involved immigration, and Bannon huddled with fellow anti-immigration hardliners like Jeff Sessions and Stephen Miller to craft their details — with hardly any consultation from the agencies that would implement them or the lawyers who’d be tasked with defending them in court.

But in the end, one order towered above the rest in importance — the travel ban. The order Bannon’s team drew up was remarkably extreme in both substance and execution, and threw airports all over the country into chaos. It led to the sudden detention of hundreds of people and many others being turned away from flights or sent back out of the US after landing there. It also led to massive, spontaneous protests across the country and, eventually, the courts stepping in to block it. (A greatly scaled-back version went into effect months later.)

The travel ban fiasco defined the beginning of the Trump presidency, overshadowing everything else he tried to do and poisoning any attempts at outreach he might have hoped to make.

It also fed a narrative that Bannon, not Trump, was truly pulling the strings in the White House — a narrative the president didn’t like very much. So Bannon was reined in somewhat. There was to be no more blindsiding the rest of the administration with monumental executive orders. He was now clearly one adviser among many.

Bannon has spent the past few months waging war against his rivals in the administration

Bannon then transitioned from shock and awe to something more like trench warfare — he and his “nationalists,” against people he viewed as his rivals in the administration, whom he referred to with the epithet “globalists.”

Publicly, Bannon has styled his role as trying to make sure Trump sticks to his campaign platform against establishment-oriented advisers who are trying to steer him in a more conventional direction. And this means a lot of conflict.

On trade policy, he wanted tougher measures against China but faced opposition from National Economic Council director Gary Cohn, the former Goldman Sachs COO. “That’s a fight I fight every day here,” Bannon said to Kuttner. “We’re still fighting. There’s Treasury and Gary Cohn and Goldman Sachs lobbying. We gotta do this. The president’s default position is to do it, but the apparatus is going crazy. Don’t get me wrong. It’s like, every day.”

Meanwhile, on foreign policy, Bannon has sparred with National Security Adviser H.R. McMaster. He reportedly opposed Trump’s strike in Syria in April, and has been arguing against McMaster’s recommendations to send more troops to Afghanistan. But he also claims to be using his influence with the president to get rid of lower-level State and Defense Department officials he dislikes. “I’m changing out people at East Asian Defense; I’m getting hawks in. I’m getting Susan Thornton [acting head of East Asian and Pacific Affairs] out at State,” he told Kuttner.

There have also been many reports about Bannon coming into conflict with Jared Kushner, Trump’s son-in-law and a top White House adviser. Bannon seems to view Kushner as too beholden to business and New York elite opinion on controversial matters. Their conflict started spilling out into the press in April, and is sometimes said to include Kushner’s wife, Ivanka Trump, as well.

Overall, Bannon has made many enemies in the administration. These rivals essentially view him as a mischief maker beholden to his own ideological faction rather than to the success of the administration as a whole. And fairly or not, he’s gained a reputation for leaking and trying to undermine other officials in the media.

So when John Kelly came in as chief of staff and started thinking about how he should shake up the West Wing, Bannon’s continued presence in the administration came into serious question. The New York Times reported Monday that Bannon could well be fired, and that he has been blamed for leaks. And Trump was vague on Bannon’s future at a press conference Tuesday, saying, “We’ll see what happens with Mr. Bannon.” And now he’s out.

What Bannon couldn’t do: turn the GOP left on economics

In reflecting on Bannon’s influence in the administration now that he’s headed out the door, it’s worth looking back at an excited interview he gave to journalist Michael Wolff back during the transition.

“We’re going to build an entirely new political movement,” Bannon said. He continued:

It's everything related to jobs. The conservatives are going to go crazy. I'm the guy pushing a trillion-dollar infrastructure plan. With negative interest rates throughout the world, it's the greatest opportunity to rebuild everything. Shipyards, ironworks, get them all jacked up. We're just going to throw it up against the wall and see if it sticks. It will be as exciting as the 1930s, greater than the Reagan revolution — conservatives, plus populists, in an economic nationalist movement.

If this had happened, it would have been a fascinating start to the Trump administration. Infrastructure spending polls incredibly well, meaning the new president would have begun his term with an initiative that could unify rather than divide the public. Meanwhile, Democrats (particularly those in red states) would have faced enormous pressure to work with Trump, and even holdout Republicans would likely fear getting on the wrong side of the new president.

But the White House didn’t end up doing anything like this. Instead, Bannon’s infrastructure push was relegated to the bottom of the administration’s priority list. There hasn’t been a serious, substantive push on it all year.

There were understandable reasons. New roads and bridges cost money, and Trump would need Congress to give him that money. The problem was that Republican leaders who controlled Congress simply didn’t support ramping up infrastructure spending. Meanwhile, Democrats in Congress faced powerful partisan incentives to oppose the administration, so an effort to work with them would have been risky.

So the White House decided to sign on to GOP leaders’ preferred agenda of health reform first, then tax reform — an agenda that’s now in shambles.

Much of the rest of Bannon’s hoped-for economic nationalist agenda has fallen by the wayside too. Trump has put the kibosh on major new multilateral trade deals, but hasn’t yet done much to roll back the existing status quo (advisers have warned him that tougher measures against China could start a trade war). Bannon’s reported suggestions that Trump back a tax increase on the wealthy have also been ignored. The result is that when it comes to economics, Trump’s administration has looked a lot more conventionally Republican than Bannon would have preferred.

Bannon’s departure will likely change the administration most in lower-profile ways

We certainly shouldn’t expect the spirit of the Trump administration to greatly change now that Bannon is departing. The president himself has repeatedly demonstrated that his own instincts on racial controversies are much like Bannon’s. And Bannon has gotten like-minded people into prominent administration jobs — for instance, fellow immigration hardliners Sessions and Miller will continue to guide policy there.

Still, with Bannon’s exit, Trump really is losing a high-level adviser who was deeply committed to operationalizing — rather than watering down — some of the most controversial parts of his agenda.

Again, while President Trump may share Bannon’s instincts on many matters, he has little interest in policy details or lower-level personnel appointments. Bannon was greatly interested in both, and worked hard to try to ensure that they complied with his “nationalist” views.

Trump could get someone else to fill a similar role (Stephen Miller seems an obvious candidate). But it’s also possible that, beyond Trump’s tweets and top-level decisions, the administration could drift in a more establishment-oriented direction on some fronts without Bannon there to wage lower-profile fights. Who will keep pushing against the tide on trade policy, or try to veto lower-level agency appointments?

The bigger picture, though, is that after seven months of the Trump administration under chief strategist Steve Bannon, the president’s approval rating is down at 37 percent. That’s hardly all Bannon’s fault — he was a skeptic of the health care push and doesn’t seem to be embroiled in the Russia scandal.

Still, much of Trump’s failure to start off his presidency on a more positive and popular footing should indeed be laid at Bannon’s feet. Bannon has often seemed more focused on pleasing the Breitbart base and waging war against his own enemies than on making Trump a successful and broadly popular president. So with a chief strategist like that, it’s no surprise that Trump has ended up largely unsuccessful and unpopular.