President Trump's enemies like to say he is losing his mind. Even his allies now must wonder if he is losing his brains.

Julius Krein, editor of the pro-Trump journal American Affairs, exasperatedly declared he was done supporting the president. "[A]fter more than 200 days in office, Mr. Trump's behavior grows only more reprehensible," he complained. "Meanwhile, his administration has no significant legislative accomplishments — and no apparent plan to deliver any."

In a more significant development, chief strategist Steve Bannon was out at the White House the very next day. "Strategist" didn't really describe Bannon's role. The on-again, off-again Breitbart leader was the Trump administration's house ideologue. As such, he was different than Valerie Jarrett, Karl Rove, or even Lee Atwater, all politicos who were personally loyal to the presidents who broad them aboard. Bannon was more committed to a specific set of ideas.

Krein was a rare intellectual supporting Trump from outside the White House. Bannon was the main intellectual working for the president from the inside. If Rove was George W. Bush's brain, they could plausibly make similar claims to be Trump's.

Trump hates this kind of talk. He may not even know Krein's name. He does know "that fucking Steve Bannon" — he even vouched for Bannon personally during his disastrous Tuesday press conference — and by all accounts bristles at the notion he owes either his election or his populist agenda to some evil genius who has bounced from Goldman Sachs to conservative news sites.

The man has a point. It was Trump, not Bannon, who bet he could win the presidency by mainly relying on earned media when all the political professionals said he couldn't. It was Trump's celebrity and charisma that made Jeb Bush, Marco Rubio, and ultimately Hillary Clinton look small. Trump wrapped up the Republican presidential nomination before Bannon joined the campaign.

All true. And yet also beside the point. Bannon, along with Jeff Sessions and Stephen Miller, helped fashion a coherent agenda out of Trump's instincts. Trump has been worried about foreigners disrespecting America and cheating our workers through bad trade deals since at least the 1980s. But that was only one piece of the puzzle.

Even if he has exaggerated his prescience on the Iraq war, Trump is less reflexively committed nation-building abroad than many other Republicans. He needed to develop that into something approaching a systematic "America First" foreign policy. Trump was also a convert on immigration, moving from believing Mitt Romney was too harsh to leading "Build the wall!" chants at campaign rallies.

Trump didn't get all of that from Bannon. Both David Frum on the center-right and Peter Beinart on the Left have credited Ann Coulter with changing Trump's mind on immigration, although his formal campaign plan on the issue borrowed heavily from Sessions and Miller.

Without Bannon and his allies, Trump's nationalism and populism in the talk of the guy at the end of the bar. It is not a program that could be put in place by the federal government. Trump can complain about the Trans-Pacific Partnership or illegal immigration. He had only a small group of advisers willing to help transform those complaints into substantive policy.

Bannon is not the only person who helped Trump discover "Trumpism," but he is arguably the most important one. He entered the White House with the same stature as chief of staff Reince Priebus, the chief representative of the Republican establishment, and left-leaning family members Jared Kushner and Ivanka Trump.

Now Bannon and Priebus are both gone, while "Javanka" remain. It is not a given that Trump will backslide on the nationalism and populism that defined his platform. New White House chief of staff John Kelly enforced a hard line on immigration and borders at the Department of Homeland Security. Sessions once again seems safely ensconced at the Department of Justice.

It is easy to imagine a more centrist administration populated with Trump's CEO buddies. (Harder to see Trump actually winning the election that way.) After Charlottesville, Va., most of those business community friends are gone and they aren't likely to come back. In the former chief strategist's waning days at the White House, Trump sounded more like Bannon than Kelly.

Nevertheless, Bannon's plaintive cry that the Trump presidency he fought for is over isn't just his characteristic hyperbole. There is no guarantee that enough of the people Bannon left behind will push for the policies that are the reason he, Krein or for that matter Peter Thiel supported Trump in the first place.

Most of the administration's work remains unfinished. We have yet to discover this White House's doers. Its thinkers have already left the building.